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 $57.39   3.612%   $59.4629   $59.46   $59.45   $59.50  
  Purchase #2 $155.32   7.168%   $166.4533   $166.45   $166.45   $166.50  
  Purchase #3 $13.53   8.299%   $14.6529   $14.65   $14.65   $14.70  
  Purchase #4 $119.92   8.821%   $130.4981   $130.50   $130.50   $130.50  
  Purchase #5 $16.41   9.649%   $17.9934   $17.99   $18.00   $18.00  
  Purchase #6 $158.35   9.468%   $173.3426   $173.34   $173.35   $173.30  
  Purchase #7 $182.72   5.769%   $193.2611   $193.26   $193.25   $193.30  
  7 purchase totals = $703.64       $755.6643   $755.65   $755.65   $755.80