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 $152.37   12.342%   $171.1755   $171.18   $171.20   $171.20  
  Purchase #2 $218.60   10.110%   $240.7005   $240.70   $240.70   $240.70  
  Purchase #3 $51.66   6.482%   $55.0086   $55.01   $55.00   $55.00  
  Purchase #4 $219.87   6.670%   $234.5353   $234.54   $234.55   $234.50  
  Purchase #5 $57.68   11.614%   $64.379   $64.38   $64.40   $64.40  
  Purchase #6 $93.67   10.247%   $103.2684   $103.27   $103.25   $103.30  
  Purchase #7 $247.61   12.556%   $278.6999   $278.70   $278.70   $278.70  
  7 purchase totals = $1,041.46       $1,147.7672   $1,147.78   $1,147.80   $1,147.80