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 $55.50   7.802%   $59.8301   $59.83   $59.85   $59.80  
  Purchase #2 $40.63   3.275%   $41.9606   $41.96   $41.95   $42.00  
  Purchase #3 $32.96   10.413%   $36.3921   $36.39   $36.40   $36.40  
  Purchase #4 $63.37   5.795%   $67.0423   $67.04   $67.05   $67.00  
  Purchase #5 $182.61   3.685%   $189.3392   $189.34   $189.35   $189.30  
  Purchase #6 $76.47   9.160%   $83.4747   $83.47   $83.45   $83.50  
  Purchase #7 $225.37   12.685%   $253.9582   $253.96   $253.95   $254.00  
  7 purchase totals = $676.91       $731.9972   $731.99   $732.00   $732.00