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 $104.63   13.792%   $119.0606   $119.06   $119.05   $119.10  
  Purchase #2 $21.69   3.463%   $22.4411   $22.44   $22.45   $22.40  
  Purchase #3 $248.91   9.167%   $271.7276   $271.73   $271.75   $271.70  
  Purchase #4 $150.95   10.309%   $166.5114   $166.51   $166.50   $166.50  
  Purchase #5 $157.62   13.334%   $178.6371   $178.64   $178.65   $178.60  
  Purchase #6 $103.42   12.503%   $116.3506   $116.35   $116.35   $116.40  
  Purchase #7 $77.29   13.433%   $87.6724   $87.67   $87.65   $87.70  
  7 purchase totals = $864.51       $962.4008   $962.40   $962.40   $962.40