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 $55.71   4.726%   $58.3429   $58.34   $58.35   $58.30  
  Purchase #2 $213.75   9.861%   $234.8279   $234.83   $234.85   $234.80  
  Purchase #3 $250.66   10.296%   $276.468   $276.47   $276.45   $276.50  
  Purchase #4 $122.81   4.728%   $128.6165   $128.62   $128.60   $128.60  
  Purchase #5 $91.51   3.281%   $94.5124   $94.51   $94.50   $94.50  
  Purchase #6 $38.26   10.777%   $42.3833   $42.38   $42.40   $42.40  
  Purchase #7 $186.89   7.120%   $200.1966   $200.20   $200.20   $200.20  
  7 purchase totals = $959.59       $1,035.3476   $1,035.35   $1,035.35   $1,035.30