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 $248.53   10.233%   $273.9621   $273.96   $273.95   $274.00  
  Purchase #2 $246.87   9.209%   $269.6043   $269.60   $269.60   $269.60  
  Purchase #3 $16.62   10.482%   $18.3621   $18.36   $18.35   $18.40  
  Purchase #4 $48.78   7.604%   $52.4892   $52.49   $52.50   $52.50  
  Purchase #5 $248.33   9.610%   $272.1945   $272.19   $272.20   $272.20  
  Purchase #6 $233.39   5.378%   $245.9417   $245.94   $245.95   $245.90  
  Purchase #7 $112.83   10.316%   $124.4695   $124.47   $124.45   $124.50  
  7 purchase totals = $1,155.35       $1,257.0234   $1,257.01   $1,257.00   $1,257.10