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 $232.79   5.806%   $246.3058   $246.31   $246.30   $246.30  
  Purchase #2 $36.25   10.374%   $40.0106   $40.01   $40.00   $40.00  
  Purchase #3 $26.72   12.148%   $29.9659   $29.97   $29.95   $30.00  
  Purchase #4 $110.59   6.272%   $117.5262   $117.53   $117.55   $117.50  
  Purchase #5 $168.78   8.206%   $182.6301   $182.63   $182.65   $182.60  
  Purchase #6 $46.70   4.107%   $48.618   $48.62   $48.60   $48.60  
  Purchase #7 $139.25   11.107%   $154.7165   $154.72   $154.70   $154.70  
  7 purchase totals = $761.08       $819.7731   $819.79   $819.75   $819.70