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 $201.82   12.731%   $227.5137   $227.51   $227.50   $227.50  
  Purchase #2 $128.53   12.536%   $144.6425   $144.64   $144.65   $144.60  
  Purchase #3 $26.86   8.581%   $29.1649   $29.16   $29.15   $29.20  
  Purchase #4 $221.86   9.137%   $242.1313   $242.13   $242.15   $242.10  
  Purchase #5 $64.88   5.820%   $68.656   $68.66   $68.65   $68.70  
  Purchase #6 $140.99   8.255%   $152.6287   $152.63   $152.65   $152.60  
  Purchase #7 $70.53   4.769%   $73.8936   $73.89   $73.90   $73.90  
  7 purchase totals = $855.47       $938.6307   $938.62   $938.65   $938.60