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 $24.76   10.355%   $27.3239   $27.32   $27.30   $27.30  
  Purchase #2 $174.63   11.140%   $194.0838   $194.08   $194.10   $194.10  
  Purchase #3 $153.64   8.298%   $166.389   $166.39   $166.40   $166.40  
  Purchase #4 $112.76   3.754%   $116.993   $116.99   $117.00   $117.00  
  Purchase #5 $185.34   12.840%   $209.1377   $209.14   $209.15   $209.10  
  Purchase #6 $90.97   8.735%   $98.9162   $98.92   $98.90   $98.90  
  Purchase #7 $43.84   11.286%   $48.7878   $48.79   $48.80   $48.80  
  7 purchase totals = $785.94       $861.6314   $861.63   $861.65   $861.60