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 $132.51   10.708%   $146.6992   $146.70   $146.70   $146.70  
  Purchase #2 $245.26   12.527%   $275.9837   $275.98   $276.00   $276.00  
  Purchase #3 $179.41   9.119%   $195.7704   $195.77   $195.75   $195.80  
  Purchase #4 $140.38   6.610%   $149.6591   $149.66   $149.65   $149.70  
  Purchase #5 $232.78   12.308%   $261.4306   $261.43   $261.45   $261.40  
  Purchase #6 $241.90   12.405%   $271.9077   $271.91   $271.90   $271.90  
  Purchase #7 $207.75   8.194%   $224.773   $224.77   $224.75   $224.80  
  7 purchase totals = $1,379.99       $1,526.2237   $1,526.22   $1,526.20   $1,526.30