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 $10.35   5.616%   $10.9313   $10.93   $10.95   $10.90  
  Purchase #2 $11.36   11.768%   $12.6968   $12.70   $12.70   $12.70  
  Purchase #3 $89.99   13.485%   $102.1252   $102.13   $102.15   $102.10  
  Purchase #4 $238.49   9.773%   $261.7976   $261.80   $261.80   $261.80  
  Purchase #5 $170.32   3.628%   $176.4992   $176.50   $176.50   $176.50  
  Purchase #6 $92.88   4.530%   $97.0875   $97.09   $97.10   $97.10  
  Purchase #7 $138.34   8.563%   $150.1861   $150.19   $150.20   $150.20  
  7 purchase totals = $751.73       $811.3237   $811.34   $811.40   $811.30