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 $190.93   11.869%   $213.5915   $213.59   $213.60   $213.60  
  Purchase #2 $49.43   12.333%   $55.5262   $55.53   $55.55   $55.50  
  Purchase #3 $58.62   10.777%   $64.9375   $64.94   $64.95   $64.90  
  Purchase #4 $102.28   12.622%   $115.1898   $115.19   $115.20   $115.20  
  Purchase #5 $205.48   4.400%   $214.5211   $214.52   $214.50   $214.50  
  Purchase #6 $44.30   5.578%   $46.7711   $46.77   $46.75   $46.80  
  Purchase #7 $49.39   11.548%   $55.0936   $55.09   $55.10   $55.10  
  7 purchase totals = $700.43       $765.6308   $765.63   $765.65   $765.60