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 $148.60   10.258%   $163.8434   $163.84   $163.85   $163.80  
  Purchase #2 $68.57   9.468%   $75.0622   $75.06   $75.05   $75.10  
  Purchase #3 $207.77   8.187%   $224.7801   $224.78   $224.80   $224.80  
  Purchase #4 $48.51   13.114%   $54.8716   $54.87   $54.85   $54.90  
  Purchase #5 $138.64   7.701%   $149.3167   $149.32   $149.30   $149.30  
  Purchase #6 $168.95   4.848%   $177.1407   $177.14   $177.15   $177.10  
  Purchase #7 $86.94   13.729%   $98.876   $98.88   $98.90   $98.90  
  7 purchase totals = $867.98       $943.8907   $943.89   $943.90   $943.90