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 $243.75   7.453%   $261.9167   $261.92   $261.90   $261.90  
  Purchase #2 $186.63   9.847%   $205.0075   $205.01   $205.00   $205.00  
  Purchase #3 $5.95   10.863%   $6.5963   $6.60   $6.60   $6.60  
  Purchase #4 $77.48   7.825%   $83.5428   $83.54   $83.55   $83.50  
  Purchase #5 $140.76   10.167%   $155.0711   $155.07   $155.05   $155.10  
  Purchase #6 $8.61   5.707%   $9.1014   $9.10   $9.10   $9.10  
  Purchase #7 $181.89   7.194%   $194.9752   $194.98   $195.00   $195.00  
  7 purchase totals = $845.07       $916.2110   $916.22   $916.20   $916.20