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 $192.36   7.322%   $206.4446   $206.44   $206.45   $206.40  
  Purchase #2 $199.89   9.480%   $218.8396   $218.84   $218.85   $218.80  
  Purchase #3 $83.71   13.215%   $94.7723   $94.77   $94.75   $94.80  
  Purchase #4 $152.63   3.164%   $157.4592   $157.46   $157.45   $157.50  
  Purchase #5 $147.37   4.775%   $154.4069   $154.41   $154.40   $154.40  
  Purchase #6 $55.29   12.394%   $62.1426   $62.14   $62.15   $62.10  
  Purchase #7 $112.56   4.818%   $117.9831   $117.98   $118.00   $118.00  
  7 purchase totals = $943.81       $1,012.0483   $1,012.04   $1,012.05   $1,012.00