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 $216.35   13.327%   $245.183   $245.18   $245.20   $245.20  
  Purchase #2 $37.77   6.329%   $40.1605   $40.16   $40.15   $40.20  
  Purchase #3 $19.85   10.584%   $21.9509   $21.95   $21.95   $22.00  
  Purchase #4 $225.93   11.591%   $252.1175   $252.12   $252.10   $252.10  
  Purchase #5 $62.33   6.624%   $66.4587   $66.46   $66.45   $66.50  
  Purchase #6 $91.25   4.470%   $95.3289   $95.33   $95.35   $95.30  
  Purchase #7 $13.53   4.215%   $14.1003   $14.10   $14.10   $14.10  
  7 purchase totals = $667.01       $735.2998   $735.30   $735.30   $735.40