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 $46.55   13.842%   $52.9935   $52.99   $53.00   $53.00  
  Purchase #2 $158.50   11.757%   $177.1348   $177.13   $177.15   $177.10  
  Purchase #3 $178.43   11.744%   $199.3848   $199.38   $199.40   $199.40  
  Purchase #4 $218.41   4.448%   $228.1249   $228.12   $228.10   $228.10  
  Purchase #5 $224.97   6.760%   $240.178   $240.18   $240.20   $240.20  
  Purchase #6 $104.28   13.663%   $118.5278   $118.53   $118.55   $118.50  
  Purchase #7 $64.71   5.525%   $68.2852   $68.29   $68.30   $68.30  
  7 purchase totals = $995.85       $1,084.6290   $1,084.62   $1,084.70   $1,084.60