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 $103.72   10.848%   $114.9715   $114.97   $114.95   $115.00  
  Purchase #2 $223.91   13.548%   $254.2453   $254.25   $254.25   $254.20  
  Purchase #3 $119.96   5.195%   $126.1919   $126.19   $126.20   $126.20  
  Purchase #4 $59.68   4.346%   $62.2737   $62.27   $62.25   $62.30  
  Purchase #5 $13.95   7.315%   $14.9704   $14.97   $14.95   $15.00  
  Purchase #6 $34.92   12.815%   $39.395   $39.40   $39.40   $39.40  
  Purchase #7 $118.70   4.608%   $124.1697   $124.17   $124.15   $124.20  
  7 purchase totals = $674.84       $736.2175   $736.22   $736.15   $736.30