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 $61.64   11.391%   $68.6614   $68.66   $68.65   $68.70  
  Purchase #2 $120.71   10.163%   $132.9778   $132.98   $133.00   $133.00  
  Purchase #3 $61.37   10.805%   $68.001   $68.00   $68.00   $68.00  
  Purchase #4 $20.26   13.756%   $23.047   $23.05   $23.05   $23.00  
  Purchase #5 $137.85   9.211%   $150.5474   $150.55   $150.55   $150.50  
  Purchase #6 $92.49   5.421%   $97.5039   $97.50   $97.50   $97.50  
  Purchase #7 $21.77   9.790%   $23.9013   $23.90   $23.90   $23.90  
  7 purchase totals = $516.09       $564.6398   $564.64   $564.65   $564.60