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	$25.57	11.553%	$28.5241	$28.52	$28.50	$28.50
Purchase #2	$147.52	11.609%	$164.6456	$164.65	$164.65	$164.60
Purchase #3	$100.67	4.634%	$105.335	$105.34	$105.35	$105.30
Purchase #4	$79.33	3.839%	$82.3755	$82.38	$82.40	$82.40
Purchase #5	$224.50	9.204%	$245.163	$245.16	$245.15	$245.20
Purchase #6	$221.90	12.538%	$249.7218	$249.72	$249.70	$249.70
Purchase #7	$116.57	8.326%	$126.2756	$126.28	$126.30	$126.30
7 purchase totals =	$916.06		$1,002.0406	$1,002.05	$1,002.05	$1,002.00