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 $104.30   11.167%   $115.9472   $115.95   $115.95   $115.90  
  Purchase #2 $244.53   7.146%   $262.0041   $262.00   $262.00   $262.00  
  Purchase #3 $173.61   7.176%   $186.0683   $186.07   $186.05   $186.10  
  Purchase #4 $240.30   6.509%   $255.9411   $255.94   $255.95   $255.90  
  Purchase #5 $172.70   10.538%   $190.8991   $190.90   $190.90   $190.90  
  Purchase #6 $101.53   12.211%   $113.9278   $113.93   $113.95   $113.90  
  Purchase #7 $109.48   9.570%   $119.9572   $119.96   $119.95   $120.00  
  7 purchase totals = $1,146.45       $1,244.7448   $1,244.75   $1,244.75   $1,244.70