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 $65.95   3.344%   $68.1554   $68.16   $68.15   $68.20  
  Purchase #2 $21.66   10.534%   $23.9417   $23.94   $23.95   $23.90  
  Purchase #3 $184.30   13.837%   $209.8016   $209.80   $209.80   $209.80  
  Purchase #4 $89.49   5.772%   $94.6554   $94.66   $94.65   $94.70  
  Purchase #5 $63.95   12.682%   $72.0601   $72.06   $72.05   $72.10  
  Purchase #6 $245.99   10.431%   $271.6492   $271.65   $271.65   $271.60  
  Purchase #7 $13.99   5.449%   $14.7523   $14.75   $14.75   $14.80  
  7 purchase totals = $685.33       $755.0157   $755.02   $755.00   $755.10