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 $38.45   8.157%   $41.5864   $41.59   $41.60   $41.60  
  Purchase #2 $228.55   11.123%   $253.9716   $253.97   $253.95   $254.00  
  Purchase #3 $49.29   10.205%   $54.32   $54.32   $54.30   $54.30  
  Purchase #4 $50.83   10.563%   $56.1992   $56.20   $56.20   $56.20  
  Purchase #5 $206.88   4.704%   $216.6116   $216.61   $216.60   $216.60  
  Purchase #6 $86.70   5.692%   $91.635   $91.64   $91.65   $91.60  
  Purchase #7 $206.97   3.339%   $213.8807   $213.88   $213.90   $213.90  
  7 purchase totals = $867.67       $928.2045   $928.21   $928.20   $928.20