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 $47.67   8.479%   $51.7119   $51.71   $51.70   $51.70  
  Purchase #2 $115.37   3.613%   $119.5383   $119.54   $119.55   $119.50  
  Purchase #3 $59.88   5.536%   $63.195   $63.20   $63.20   $63.20  
  Purchase #4 $131.79   8.245%   $142.6561   $142.66   $142.65   $142.70  
  Purchase #5 $230.63   5.835%   $244.0873   $244.09   $244.10   $244.10  
  Purchase #6 $217.41   3.698%   $225.4498   $225.45   $225.45   $225.40  
  Purchase #7 $112.39   5.426%   $118.4883   $118.49   $118.50   $118.50  
  7 purchase totals = $915.14       $965.1267   $965.14   $965.15   $965.10