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 $215.89   8.590%   $234.435   $234.44   $234.45   $234.40  
  Purchase #2 $36.58   11.486%   $40.7816   $40.78   $40.80   $40.80  
  Purchase #3 $30.71   6.502%   $32.7068   $32.71   $32.70   $32.70  
  Purchase #4 $201.61   8.821%   $219.394   $219.39   $219.40   $219.40  
  Purchase #5 $183.74   6.261%   $195.244   $195.24   $195.25   $195.20  
  Purchase #6 $250.79   13.545%   $284.7595   $284.76   $284.75   $284.80  
  Purchase #7 $244.64   8.310%   $264.9696   $264.97   $264.95   $265.00  
  7 purchase totals = $1,163.96       $1,272.2905   $1,272.29   $1,272.30   $1,272.30