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 $58.90   13.675%   $66.9546   $66.95   $66.95   $67.00  
  Purchase #2 $134.54   13.870%   $153.2007   $153.20   $153.20   $153.20  
  Purchase #3 $79.42   11.841%   $88.8241   $88.82   $88.80   $88.80  
  Purchase #4 $32.41   13.344%   $36.7348   $36.73   $36.75   $36.70  
  Purchase #5 $227.73   13.373%   $258.1843   $258.18   $258.20   $258.20  
  Purchase #6 $68.49   11.801%   $76.5725   $76.57   $76.55   $76.60  
  Purchase #7 $179.93   8.500%   $195.2241   $195.22   $195.20   $195.20  
  7 purchase totals = $781.42       $875.6951   $875.67   $875.65   $875.70