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 $65.47   12.388%   $73.5804   $73.58   $73.60   $73.60  
  Purchase #2 $242.79   4.158%   $252.8852   $252.89   $252.90   $252.90  
  Purchase #3 $244.29   12.542%   $274.9289   $274.93   $274.95   $274.90  
  Purchase #4 $88.67   8.494%   $96.2016   $96.20   $96.20   $96.20  
  Purchase #5 $187.51   4.612%   $196.158   $196.16   $196.15   $196.20  
  Purchase #6 $40.86   13.208%   $46.2568   $46.26   $46.25   $46.30  
  Purchase #7 $57.97   7.361%   $62.2372   $62.24   $62.25   $62.20  
  7 purchase totals = $927.56       $1,002.2481   $1,002.26   $1,002.30   $1,002.30