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 $239.60   10.162%   $263.9482   $263.95   $263.95   $263.90  
  Purchase #2 $242.88   11.804%   $271.5496   $271.55   $271.55   $271.50  
  Purchase #3 $118.34   9.869%   $130.019   $130.02   $130.00   $130.00  
  Purchase #4 $203.81   9.388%   $222.9437   $222.94   $222.95   $222.90  
  Purchase #5 $237.49   4.484%   $248.1391   $248.14   $248.15   $248.10  
  Purchase #6 $6.88   11.359%   $7.6615   $7.66   $7.65   $7.70  
  Purchase #7 $195.96   4.190%   $204.1707   $204.17   $204.15   $204.20  
  7 purchase totals = $1,244.96       $1,348.4318   $1,348.43   $1,348.40   $1,348.30