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 $76.47   12.832%   $86.2826   $86.28   $86.30   $86.30  
  Purchase #2 $49.34   4.467%   $51.544   $51.54   $51.55   $51.50  
  Purchase #3 $60.36   12.106%   $67.6672   $67.67   $67.65   $67.70  
  Purchase #4 $14.87   10.114%   $16.374   $16.37   $16.35   $16.40  
  Purchase #5 $29.91   9.830%   $32.8502   $32.85   $32.85   $32.90  
  Purchase #6 $36.52   4.798%   $38.2722   $38.27   $38.25   $38.30  
  Purchase #7 $58.50   13.291%   $66.2752   $66.28   $66.30   $66.30  
  7 purchase totals = $325.97       $359.2654   $359.26   $359.25   $359.40