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 $241.51   7.301%   $259.1426   $259.14   $259.15   $259.10  
  Purchase #2 $222.56   10.852%   $246.7122   $246.71   $246.70   $246.70  
  Purchase #3 $21.51   6.762%   $22.9645   $22.96   $22.95   $23.00  
  Purchase #4 $217.43   11.304%   $242.0083   $242.01   $242.00   $242.00  
  Purchase #5 $53.32   4.790%   $55.874   $55.87   $55.85   $55.90  
  Purchase #6 $245.75   12.361%   $276.1272   $276.13   $276.15   $276.10  
  Purchase #7 $232.40   9.533%   $254.5547   $254.55   $254.55   $254.60  
  7 purchase totals = $1,234.48       $1,357.3835   $1,357.37   $1,357.35   $1,357.40