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 $211.64   4.458%   $221.0749   $221.07   $221.05   $221.10  
  Purchase #2 $197.87   12.431%   $222.4672   $222.47   $222.45   $222.50  
  Purchase #3 $243.69   5.702%   $257.5852   $257.59   $257.60   $257.60  
  Purchase #4 $16.33   5.665%   $17.2551   $17.26   $17.25   $17.30  
  Purchase #5 $232.38   5.508%   $245.1795   $245.18   $245.20   $245.20  
  Purchase #6 $161.64   13.776%   $183.9075   $183.91   $183.90   $183.90  
  Purchase #7 $213.88   10.831%   $237.0453   $237.05   $237.05   $237.00  
  7 purchase totals = $1,277.43       $1,384.5147   $1,384.53   $1,384.50   $1,384.60