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	$33.70	11.415%	$37.5469	$37.55	$37.55	$37.50
Purchase #2	$238.36	13.228%	$269.8903	$269.89	$269.90	$269.90
Purchase #3	$74.70	4.545%	$78.0951	$78.10	$78.10	$78.10
Purchase #4	$52.65	4.749%	$55.1503	$55.15	$55.15	$55.20
Purchase #5	$242.30	8.653%	$263.2662	$263.27	$263.25	$263.30
Purchase #6	$19.85	6.420%	$21.1244	$21.12	$21.10	$21.10
Purchase #7	$66.81	4.846%	$70.0476	$70.05	$70.05	$70.00
7 purchase totals =	$728.37		$795.1208	$795.13	$795.10	$795.10