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 $201.40   6.257%   $214.0016   $214.00   $214.00   $214.00  
  Purchase #2 $146.64   10.200%   $161.5973   $161.60   $161.60   $161.60  
  Purchase #3 $241.65   5.479%   $254.89   $254.89   $254.90   $254.90  
  Purchase #4 $150.63   5.717%   $159.2415   $159.24   $159.25   $159.20  
  Purchase #5 $36.59   10.338%   $40.3727   $40.37   $40.35   $40.40  
  Purchase #6 $54.93   9.526%   $60.1626   $60.16   $60.15   $60.20  
  Purchase #7 $58.70   12.511%   $66.044   $66.04   $66.05   $66.00  
  7 purchase totals = $890.54       $956.3097   $956.30   $956.30   $956.30