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	$83.28	9.516%	$91.2049	$91.20	$91.20	$91.20
Purchase #2	$153.90	6.194%	$163.4326	$163.43	$163.45	$163.40
Purchase #3	$90.28	11.297%	$100.4789	$100.48	$100.50	$100.50
Purchase #4	$50.76	6.754%	$54.1883	$54.19	$54.20	$54.20
Purchase #5	$216.41	12.621%	$243.7231	$243.72	$243.70	$243.70
Purchase #6	$133.69	8.299%	$144.7849	$144.78	$144.80	$144.80
Purchase #7	$60.71	3.380%	$62.762	$62.76	$62.75	$62.80
7 purchase totals =	$789.03		$860.5747	$860.56	$860.60	$860.60