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	$16.77	6.313%	$17.8287	$17.83	$17.85	$17.80
Purchase #2	$98.87	12.796%	$111.5214	$111.52	$111.50	$111.50
Purchase #3	$17.44	5.797%	$18.451	$18.45	$18.45	$18.50
Purchase #4	$71.87	6.430%	$76.4912	$76.49	$76.50	$76.50
Purchase #5	$41.91	8.150%	$45.3257	$45.33	$45.35	$45.30
Purchase #6	$238.41	9.194%	$260.3294	$260.33	$260.35	$260.30
Purchase #7	$45.51	11.791%	$50.8761	$50.88	$50.90	$50.90
7 purchase totals =	$530.78		$580.8235	$580.83	$580.90	$580.80