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	$23.40	9.375%	$25.5938	$25.59	$25.60	$25.60
Purchase #2	$145.37	6.266%	$154.4789	$154.48	$154.50	$154.50
Purchase #3	$68.27	13.537%	$77.5117	$77.51	$77.50	$77.50
Purchase #4	$83.48	8.769%	$90.8004	$90.80	$90.80	$90.80
Purchase #5	$155.53	9.821%	$170.8046	$170.80	$170.80	$170.80
Purchase #6	$56.57	9.861%	$62.1484	$62.15	$62.15	$62.10
Purchase #7	$106.86	11.574%	$119.228	$119.23	$119.25	$119.20
7 purchase totals =	$639.48		$700.5658	$700.56	$700.60	$700.50