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 $220.34   4.430%   $230.1011   $230.10   $230.10   $230.10  
  Purchase #2 $177.49   12.106%   $198.9769   $198.98   $199.00   $199.00  
  Purchase #3 $227.38   6.752%   $242.7327   $242.73   $242.75   $242.70  
  Purchase #4 $90.72   7.584%   $97.6002   $97.60   $97.60   $97.60  
  Purchase #5 $130.27   10.331%   $143.7282   $143.73   $143.75   $143.70  
  Purchase #6 $17.30   5.631%   $18.2742   $18.27   $18.25   $18.30  
  Purchase #7 $29.74   7.352%   $31.9265   $31.93   $31.95   $31.90  
  7 purchase totals = $893.24       $963.3398   $963.34   $963.40   $963.30