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 $110.71   13.361%   $125.502   $125.50   $125.50   $125.50  
  Purchase #2 $94.56   3.154%   $97.5424   $97.54   $97.55   $97.50  
  Purchase #3 $240.27   10.426%   $265.3206   $265.32   $265.30   $265.30  
  Purchase #4 $145.64   5.276%   $153.324   $153.32   $153.30   $153.30  
  Purchase #5 $238.37   9.792%   $261.7112   $261.71   $261.70   $261.70  
  Purchase #6 $41.84   9.317%   $45.7382   $45.74   $45.75   $45.70  
  Purchase #7 $14.73   13.503%   $16.719   $16.72   $16.70   $16.70  
  7 purchase totals = $886.12       $965.8574   $965.85   $965.80   $965.70