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 $208.27   13.558%   $236.5072   $236.51   $236.50   $236.50  
  Purchase #2 $127.48   11.645%   $142.325   $142.33   $142.35   $142.30  
  Purchase #3 $154.53   13.542%   $175.4565   $175.46   $175.45   $175.50  
  Purchase #4 $55.27   6.282%   $58.7421   $58.74   $58.75   $58.70  
  Purchase #5 $68.62   10.222%   $75.6343   $75.63   $75.65   $75.60  
  Purchase #6 $69.36   7.439%   $74.5197   $74.52   $74.50   $74.50  
  Purchase #7 $27.60   10.529%   $30.506   $30.51   $30.50   $30.50  
  7 purchase totals = $711.13       $793.6908   $793.70   $793.70   $793.60