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 $58.72   7.216%   $62.9572   $62.96   $62.95   $63.00  
  Purchase #2 $228.35   11.630%   $254.9071   $254.91   $254.90   $254.90  
  Purchase #3 $140.32   5.654%   $148.2537   $148.25   $148.25   $148.30  
  Purchase #4 $178.59   5.173%   $187.8285   $187.83   $187.85   $187.80  
  Purchase #5 $101.85   13.590%   $115.6914   $115.69   $115.70   $115.70  
  Purchase #6 $214.26   4.823%   $224.5938   $224.59   $224.60   $224.60  
  Purchase #7 $21.71   8.106%   $23.4698   $23.47   $23.45   $23.50  
  7 purchase totals = $943.80       $1,017.7015   $1,017.70   $1,017.70   $1,017.80