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 $32.86   13.544%   $37.3106   $37.31   $37.30   $37.30  
  Purchase #2 $90.85   11.543%   $101.3368   $101.34   $101.35   $101.30  
  Purchase #3 $106.49   7.394%   $114.3639   $114.36   $114.35   $114.40  
  Purchase #4 $119.80   4.523%   $125.2186   $125.22   $125.20   $125.20  
  Purchase #5 $169.99   6.808%   $181.5629   $181.56   $181.55   $181.60  
  Purchase #6 $86.73   13.788%   $98.6883   $98.69   $98.70   $98.70  
  Purchase #7 $154.74   8.817%   $168.3834   $168.38   $168.40   $168.40  
  7 purchase totals = $761.46       $826.8645   $826.86   $826.85   $826.90