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	$85.88	3.771%	$89.1185	$89.12	$89.10	$89.10
Purchase #2	$196.52	11.665%	$219.4441	$219.44	$219.45	$219.40
Purchase #3	$200.62	11.361%	$223.4124	$223.41	$223.40	$223.40
Purchase #4	$33.34	13.504%	$37.8422	$37.84	$37.85	$37.80
Purchase #5	$46.42	4.506%	$48.5117	$48.51	$48.50	$48.50
Purchase #6	$199.56	8.619%	$216.7601	$216.76	$216.75	$216.80
Purchase #7	$145.56	5.403%	$153.4246	$153.42	$153.40	$153.40
7 purchase totals =	$907.90		$988.5136	$988.50	$988.45	$988.40