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 $56.66   9.686%   $62.1481   $62.15   $62.15   $62.10  
  Purchase #2 $187.36   6.217%   $199.0082   $199.01   $199.00   $199.00  
  Purchase #3 $82.95   3.221%   $85.6218   $85.62   $85.60   $85.60  
  Purchase #4 $103.55   12.427%   $116.4182   $116.42   $116.40   $116.40  
  Purchase #5 $62.96   7.355%   $67.5907   $67.59   $67.60   $67.60  
  Purchase #6 $217.92   6.183%   $231.394   $231.39   $231.40   $231.40  
  Purchase #7 $188.47   4.750%   $197.4223   $197.42   $197.40   $197.40  
  7 purchase totals = $899.87       $959.6033   $959.60   $959.55   $959.50