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	$18.37	5.259%	$19.3361	$19.34	$19.35	$19.30
Purchase #2	$155.29	11.224%	$172.7197	$172.72	$172.70	$172.70
Purchase #3	$104.38	10.640%	$115.486	$115.49	$115.50	$115.50
Purchase #4	$242.62	4.473%	$253.4724	$253.47	$253.45	$253.50
Purchase #5	$112.78	9.462%	$123.4512	$123.45	$123.45	$123.50
Purchase #6	$21.66	10.244%	$23.8789	$23.88	$23.90	$23.90
Purchase #7	$86.72	3.502%	$89.7569	$89.76	$89.75	$89.80
7 purchase totals =	$741.82		$798.1012	$798.11	$798.10	$798.20