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 $68.79   11.262%   $76.5371   $76.54   $76.55   $76.50  
  Purchase #2 $90.28   9.361%   $98.7311   $98.73   $98.75   $98.70  
  Purchase #3 $153.85   4.306%   $160.4748   $160.47   $160.45   $160.50  
  Purchase #4 $74.27   8.585%   $80.6461   $80.65   $80.65   $80.60  
  Purchase #5 $92.32   10.412%   $101.9324   $101.93   $101.95   $101.90  
  Purchase #6 $21.37   9.243%   $23.3452   $23.35   $23.35   $23.30  
  Purchase #7 $45.71   9.812%   $50.1951   $50.20   $50.20   $50.20  
  7 purchase totals = $546.59       $591.8618   $591.87   $591.90   $591.70