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 $58.76   6.302%   $62.4631   $62.46   $62.45   $62.50  
  Purchase #2 $228.46   11.341%   $254.3696   $254.37   $254.35   $254.40  
  Purchase #3 $120.28   6.565%   $128.1764   $128.18   $128.20   $128.20  
  Purchase #4 $168.94   8.523%   $183.3388   $183.34   $183.35   $183.30  
  Purchase #5 $16.94   10.490%   $18.717   $18.72   $18.70   $18.70  
  Purchase #6 $182.65   13.859%   $207.9635   $207.96   $207.95   $208.00  
  Purchase #7 $121.29   13.593%   $137.7769   $137.78   $137.80   $137.80  
  7 purchase totals = $897.32       $992.8053   $992.81   $992.80   $992.90