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 $85.98   7.359%   $92.3073   $92.31   $92.30   $92.30  
  Purchase #2 $248.98   6.195%   $264.4043   $264.40   $264.40   $264.40  
  Purchase #3 $33.58   12.853%   $37.896   $37.90   $37.90   $37.90  
  Purchase #4 $72.90   3.206%   $75.2372   $75.24   $75.25   $75.20  
  Purchase #5 $17.48   6.327%   $18.586   $18.59   $18.60   $18.60  
  Purchase #6 $156.57   13.375%   $177.5112   $177.51   $177.50   $177.50  
  Purchase #7 $236.29   4.691%   $247.3744   $247.37   $247.35   $247.40  
  7 purchase totals = $851.78       $913.3164   $913.32   $913.30   $913.30