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 $207.50   9.561%   $227.3391   $227.34   $227.35   $227.30  
  Purchase #2 $233.88   5.612%   $247.0053   $247.01   $247.00   $247.00  
  Purchase #3 $58.61   7.812%   $63.1886   $63.19   $63.20   $63.20  
  Purchase #4 $60.73   5.607%   $64.1351   $64.14   $64.15   $64.10  
  Purchase #5 $44.96   12.614%   $50.6313   $50.63   $50.65   $50.60  
  Purchase #6 $120.70   9.790%   $132.5165   $132.52   $132.50   $132.50  
  Purchase #7 $61.99   6.339%   $65.9195   $65.92   $65.90   $65.90  
  7 purchase totals = $788.37       $850.7354   $850.75   $850.75   $850.60