Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $117.93   11.646%   $131.6641   $131.66   $131.65   $131.70  
  Purchase #2 $184.99   13.762%   $210.4483   $210.45   $210.45   $210.40  
  Purchase #3 $200.43   13.120%   $226.7264   $226.73   $226.75   $226.70  
  Purchase #4 $184.88   13.163%   $209.2158   $209.22   $209.20   $209.20  
  Purchase #5 $201.27   12.798%   $227.0285   $227.03   $227.05   $227.00  
  Purchase #6 $167.57   11.402%   $186.6763   $186.68   $186.70   $186.70  
  Purchase #7 $153.51   12.138%   $172.143   $172.14   $172.15   $172.10  
  7 purchase totals = $1,210.58       $1,363.9024   $1,363.91   $1,363.95   $1,363.80