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 $76.79   7.486%   $82.5385   $82.54   $82.55   $82.50  
  Purchase #2 $245.98   5.178%   $258.7168   $258.72   $258.70   $258.70  
  Purchase #3 $89.98   13.152%   $101.8142   $101.81   $101.80   $101.80  
  Purchase #4 $98.70   7.616%   $106.217   $106.22   $106.20   $106.20  
  Purchase #5 $156.63   3.448%   $162.0306   $162.03   $162.05   $162.00  
  Purchase #6 $162.80   12.373%   $182.9432   $182.94   $182.95   $182.90  
  Purchase #7 $86.32   11.862%   $96.5593   $96.56   $96.55   $96.60  
  7 purchase totals = $917.20       $990.8196   $990.82   $990.80   $990.70