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 $214.54   3.117%   $221.2272   $221.23   $221.25   $221.20  
  Purchase #2 $143.51   8.147%   $155.2018   $155.20   $155.20   $155.20  
  Purchase #3 $19.72   8.806%   $21.4565   $21.46   $21.45   $21.50  
  Purchase #4 $123.53   13.613%   $140.3461   $140.35   $140.35   $140.30  
  Purchase #5 $206.29   3.211%   $212.914   $212.91   $212.90   $212.90  
  Purchase #6 $125.84   12.737%   $141.8682   $141.87   $141.85   $141.90  
  Purchase #7 $59.68   4.807%   $62.5488   $62.55   $62.55   $62.50  
  7 purchase totals = $893.11       $955.5626   $955.57   $955.55   $955.50