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 $58.29   3.231%   $60.1733   $60.17   $60.15   $60.20  
  Purchase #2 $174.89   13.326%   $198.1958   $198.20   $198.20   $198.20  
  Purchase #3 $8.54   11.613%   $9.5318   $9.53   $9.55   $9.50  
  Purchase #4 $214.26   10.759%   $237.3122   $237.31   $237.30   $237.30  
  Purchase #5 $131.56   10.531%   $145.4146   $145.41   $145.40   $145.40  
  Purchase #6 $32.90   8.277%   $35.6231   $35.62   $35.60   $35.60  
  Purchase #7 $70.64   4.398%   $73.7467   $73.75   $73.75   $73.70  
  7 purchase totals = $691.08       $759.9975   $759.99   $759.95   $759.90