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 $209.81   13.754%   $238.6673   $238.67   $238.65   $238.70  
  Purchase #2 $131.99   11.253%   $146.8428   $146.84   $146.85   $146.80  
  Purchase #3 $173.48   5.313%   $182.697   $182.70   $182.70   $182.70  
  Purchase #4 $12.55   8.590%   $13.628   $13.63   $13.65   $13.60  
  Purchase #5 $21.30   11.463%   $23.7416   $23.74   $23.75   $23.70  
  Purchase #6 $170.95   8.512%   $185.5013   $185.50   $185.50   $185.50  
  Purchase #7 $127.32   10.353%   $140.5014   $140.50   $140.50   $140.50  
  7 purchase totals = $847.40       $931.5794   $931.58   $931.60   $931.50