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 $93.54   3.203%   $96.5361   $96.54   $96.55   $96.50  
  Purchase #2 $97.27   5.642%   $102.758   $102.76   $102.75   $102.80  
  Purchase #3 $219.79   5.854%   $232.6565   $232.66   $232.65   $232.70  
  Purchase #4 $64.73   9.265%   $70.7272   $70.73   $70.75   $70.70  
  Purchase #5 $55.77   9.679%   $61.168   $61.17   $61.15   $61.20  
  Purchase #6 $241.74   5.861%   $255.9084   $255.91   $255.90   $255.90  
  Purchase #7 $112.87   11.650%   $126.0194   $126.02   $126.00   $126.00  
  7 purchase totals = $885.71       $945.7736   $945.79   $945.75   $945.80