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 $214.99   12.223%   $241.2682   $241.27   $241.25   $241.30  
  Purchase #2 $182.31   8.318%   $197.4745   $197.47   $197.45   $197.50  
  Purchase #3 $158.63   7.277%   $170.1735   $170.17   $170.15   $170.20  
  Purchase #4 $39.71   12.780%   $44.7849   $44.78   $44.80   $44.80  
  Purchase #5 $70.60   11.419%   $78.6618   $78.66   $78.65   $78.70  
  Purchase #6 $214.34   4.292%   $223.5395   $223.54   $223.55   $223.50  
  Purchase #7 $129.78   7.844%   $139.9599   $139.96   $139.95   $140.00  
  7 purchase totals = $1,010.36       $1,095.8623   $1,095.85   $1,095.80   $1,096.00