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 $92.68   12.134%   $103.9258   $103.93   $103.95   $103.90  
  Purchase #2 $45.41   8.487%   $49.2639   $49.26   $49.25   $49.30  
  Purchase #3 $28.89   11.785%   $32.2947   $32.29   $32.30   $32.30  
  Purchase #4 $181.45   5.780%   $191.9378   $191.94   $191.95   $191.90  
  Purchase #5 $53.32   8.841%   $58.034   $58.03   $58.05   $58.00  
  Purchase #6 $40.58   4.863%   $42.5534   $42.55   $42.55   $42.60  
  Purchase #7 $129.30   9.182%   $141.1723   $141.17   $141.15   $141.20  
  7 purchase totals = $571.63       $619.1819   $619.17   $619.20   $619.20