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 $93.70   11.788%   $104.7454   $104.75   $104.75   $104.70  
  Purchase #2 $104.29   8.434%   $113.0858   $113.09   $113.10   $113.10  
  Purchase #3 $198.49   8.857%   $216.0703   $216.07   $216.05   $216.10  
  Purchase #4 $60.76   7.445%   $65.2836   $65.28   $65.30   $65.30  
  Purchase #5 $233.65   12.339%   $262.4801   $262.48   $262.50   $262.50  
  Purchase #6 $19.78   4.155%   $20.6019   $20.60   $20.60   $20.60  
  Purchase #7 $146.26   4.769%   $153.2351   $153.24   $153.25   $153.20  
  7 purchase totals = $856.93       $935.5022   $935.51   $935.55   $935.50