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 $66.89   11.447%   $74.5469   $74.55   $74.55   $74.50  
  Purchase #2 $76.98   11.853%   $86.1044   $86.10   $86.10   $86.10  
  Purchase #3 $107.37   10.102%   $118.2165   $118.22   $118.20   $118.20  
  Purchase #4 $179.93   13.725%   $204.6254   $204.63   $204.65   $204.60  
  Purchase #5 $90.28   8.158%   $97.645   $97.65   $97.65   $97.60  
  Purchase #6 $109.98   3.230%   $113.5324   $113.53   $113.55   $113.50  
  Purchase #7 $206.83   12.698%   $233.0933   $233.09   $233.10   $233.10  
  7 purchase totals = $838.26       $927.7639   $927.77   $927.80   $927.60