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 $14.53   6.585%   $15.4868   $15.49   $15.50   $15.50  
  Purchase #2 $89.73   4.412%   $93.6889   $93.69   $93.70   $93.70  
  Purchase #3 $48.34   3.441%   $50.0034   $50.00   $50.00   $50.00  
  Purchase #4 $91.74   6.473%   $97.6783   $97.68   $97.70   $97.70  
  Purchase #5 $132.83   11.117%   $147.5967   $147.60   $147.60   $147.60  
  Purchase #6 $142.43   7.695%   $153.39   $153.39   $153.40   $153.40  
  Purchase #7 $71.77   4.512%   $75.0083   $75.01   $75.00   $75.00  
  7 purchase totals = $591.37       $632.8524   $632.86   $632.90   $632.90