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 $32.82   6.763%   $35.0396   $35.04   $35.05   $35.00  
  Purchase #2 $117.72   3.206%   $121.4941   $121.49   $121.50   $121.50  
  Purchase #3 $64.50   3.478%   $66.7433   $66.74   $66.75   $66.70  
  Purchase #4 $51.73   4.538%   $54.0775   $54.08   $54.10   $54.10  
  Purchase #5 $95.37   13.183%   $107.9426   $107.94   $107.95   $107.90  
  Purchase #6 $45.67   13.528%   $51.8482   $51.85   $51.85   $51.80  
  Purchase #7 $227.57   7.794%   $245.3068   $245.31   $245.30   $245.30  
  7 purchase totals = $635.38       $682.4521   $682.45   $682.50   $682.30