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 $190.67   6.809%   $203.6527   $203.65   $203.65   $203.70  
  Purchase #2 $32.97   9.389%   $36.0656   $36.07   $36.05   $36.10  
  Purchase #3 $13.97   11.502%   $15.5768   $15.58   $15.60   $15.60  
  Purchase #4 $42.28   5.485%   $44.5991   $44.60   $44.60   $44.60  
  Purchase #5 $250.44   3.213%   $258.4866   $258.49   $258.50   $258.50  
  Purchase #6 $15.85   9.266%   $17.3187   $17.32   $17.30   $17.30  
  Purchase #7 $187.50   11.431%   $208.9331   $208.93   $208.95   $208.90  
  7 purchase totals = $733.68       $784.6326   $784.64   $784.65   $784.70