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 $226.47   11.117%   $251.6467   $251.65   $251.65   $251.60  
  Purchase #2 $111.61   4.281%   $116.388   $116.39   $116.40   $116.40  
  Purchase #3 $60.33   3.326%   $62.3366   $62.34   $62.35   $62.30  
  Purchase #4 $95.84   13.362%   $108.6461   $108.65   $108.65   $108.60  
  Purchase #5 $19.53   3.237%   $20.1622   $20.16   $20.15   $20.20  
  Purchase #6 $61.70   6.612%   $65.7796   $65.78   $65.80   $65.80  
  Purchase #7 $54.39   4.746%   $56.9713   $56.97   $56.95   $57.00  
  7 purchase totals = $629.87       $681.9305   $681.94   $681.95   $681.90