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	$159.52	4.365%	$166.483	$166.48	$166.50	$166.50
Purchase #2	$124.66	9.821%	$136.9029	$136.90	$136.90	$136.90
Purchase #3	$28.47	8.462%	$30.8791	$30.88	$30.90	$30.90
Purchase #4	$112.42	5.760%	$118.8954	$118.90	$118.90	$118.90
Purchase #5	$148.98	11.250%	$165.7403	$165.74	$165.75	$165.70
Purchase #6	$51.27	9.506%	$56.1437	$56.14	$56.15	$56.10
Purchase #7	$49.56	10.569%	$54.798	$54.80	$54.80	$54.80
7 purchase totals =	$674.88		$729.8424	$729.84	$729.90	$729.80