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 $100.45   9.635%   $110.1284   $110.13   $110.15   $110.10  
  Purchase #2 $159.56   12.411%   $179.363   $179.36   $179.35   $179.40  
  Purchase #3 $101.42   13.832%   $115.4484   $115.45   $115.45   $115.40  
  Purchase #4 $61.84   11.552%   $68.9838   $68.98   $69.00   $69.00  
  Purchase #5 $53.96   3.344%   $55.7644   $55.76   $55.75   $55.80  
  Purchase #6 $55.79   4.106%   $58.0807   $58.08   $58.10   $58.10  
  Purchase #7 $238.34   10.548%   $263.4801   $263.48   $263.50   $263.50  
  7 purchase totals = $771.36       $851.2488   $851.24   $851.30   $851.30