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 $240.59   7.348%   $258.2686   $258.27   $258.25   $258.30  
  Purchase #2 $219.90   10.846%   $243.7504   $243.75   $243.75   $243.80  
  Purchase #3 $60.95   7.642%   $65.6078   $65.61   $65.60   $65.60  
  Purchase #4 $241.43   7.870%   $260.4305   $260.43   $260.45   $260.40  
  Purchase #5 $68.98   7.654%   $74.2597   $74.26   $74.25   $74.30  
  Purchase #6 $242.88   7.523%   $261.1519   $261.15   $261.15   $261.20  
  Purchase #7 $91.42   11.383%   $101.8263   $101.83   $101.85   $101.80  
  7 purchase totals = $1,166.15       $1,265.2952   $1,265.30   $1,265.30   $1,265.40