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 $204.77   10.603%   $226.4818   $226.48   $226.50   $226.50  
  Purchase #2 $250.76   6.282%   $266.5127   $266.51   $266.50   $266.50  
  Purchase #3 $74.67   4.824%   $78.2721   $78.27   $78.25   $78.30  
  Purchase #4 $158.59   8.283%   $171.726   $171.73   $171.75   $171.70  
  Purchase #5 $109.55   8.609%   $118.9812   $118.98   $119.00   $119.00  
  Purchase #6 $234.77   8.514%   $254.7583   $254.76   $254.75   $254.80  
  Purchase #7 $54.26   12.184%   $60.871   $60.87   $60.85   $60.90  
  7 purchase totals = $1,087.37       $1,177.6031   $1,177.60   $1,177.60   $1,177.70