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 $217.73   13.113%   $246.2809   $246.28   $246.30   $246.30  
  Purchase #2 $32.68   11.450%   $36.4219   $36.42   $36.40   $36.40  
  Purchase #3 $52.67   11.357%   $58.6517   $58.65   $58.65   $58.70  
  Purchase #4 $138.56   11.179%   $154.0496   $154.05   $154.05   $154.00  
  Purchase #5 $215.39   11.736%   $240.6682   $240.67   $240.65   $240.70  
  Purchase #6 $116.88   6.216%   $124.1453   $124.15   $124.15   $124.10  
  Purchase #7 $99.79   12.743%   $112.5062   $112.51   $112.50   $112.50  
  7 purchase totals = $873.70       $972.7238   $972.73   $972.70   $972.70