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 $61.53   10.647%   $68.0811   $68.08   $68.10   $68.10  
  Purchase #2 $32.82   9.448%   $35.9208   $35.92   $35.90   $35.90  
  Purchase #3 $54.63   5.124%   $57.4292   $57.43   $57.45   $57.40  
  Purchase #4 $206.55   10.339%   $227.9052   $227.91   $227.90   $227.90  
  Purchase #5 $104.96   9.859%   $115.308   $115.31   $115.30   $115.30  
  Purchase #6 $20.94   5.706%   $22.1348   $22.13   $22.15   $22.10  
  Purchase #7 $222.68   11.173%   $247.56   $247.56   $247.55   $247.60  
  7 purchase totals = $704.11       $774.3391   $774.34   $774.35   $774.30