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 $173.27   6.619%   $184.7387   $184.74   $184.75   $184.70  
  Purchase #2 $18.76   7.195%   $20.1098   $20.11   $20.10   $20.10  
  Purchase #3 $216.64   4.630%   $226.6704   $226.67   $226.65   $226.70  
  Purchase #4 $152.33   10.694%   $168.6202   $168.62   $168.60   $168.60  
  Purchase #5 $227.45   4.272%   $237.1667   $237.17   $237.15   $237.20  
  Purchase #6 $108.26   11.826%   $121.0628   $121.06   $121.05   $121.10  
  Purchase #7 $142.27   12.413%   $159.93   $159.93   $159.95   $159.90  
  7 purchase totals = $1,038.98       $1,118.2986   $1,118.30   $1,118.25   $1,118.30