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 $180.85   12.237%   $202.9806   $202.98   $203.00   $203.00  
  Purchase #2 $95.68   5.137%   $100.5951   $100.60   $100.60   $100.60  
  Purchase #3 $21.69   7.341%   $23.2823   $23.28   $23.30   $23.30  
  Purchase #4 $201.57   12.600%   $226.9678   $226.97   $226.95   $227.00  
  Purchase #5 $69.48   9.558%   $76.1209   $76.12   $76.10   $76.10  
  Purchase #6 $129.74   9.485%   $142.0458   $142.05   $142.05   $142.00  
  Purchase #7 $247.75   5.400%   $261.1285   $261.13   $261.15   $261.10  
  7 purchase totals = $946.76       $1,033.1210   $1,033.13   $1,033.15   $1,033.10