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	$97.52	3.244%	$100.6835	$100.68	$100.70	$100.70
Purchase #2	$145.38	7.608%	$156.4405	$156.44	$156.45	$156.40
Purchase #3	$50.27	12.133%	$56.3693	$56.37	$56.35	$56.40
Purchase #4	$82.60	9.227%	$90.2215	$90.22	$90.20	$90.20
Purchase #5	$158.73	8.579%	$172.3474	$172.35	$172.35	$172.30
Purchase #6	$160.57	11.609%	$179.2106	$179.21	$179.20	$179.20
Purchase #7	$89.62	13.757%	$101.949	$101.95	$101.95	$101.90
7 purchase totals =	$784.69		$857.2218	$857.22	$857.20	$857.10