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	$64.51	8.871%	$70.2327	$70.23	$70.25	$70.20
Purchase #2	$28.48	4.761%	$29.8359	$29.84	$29.85	$29.80
Purchase #3	$223.40	6.478%	$237.8719	$237.87	$237.85	$237.90
Purchase #4	$72.51	13.687%	$82.4344	$82.43	$82.45	$82.40
Purchase #5	$118.41	7.518%	$127.3121	$127.31	$127.30	$127.30
Purchase #6	$161.77	8.562%	$175.6207	$175.62	$175.60	$175.60
Purchase #7	$138.93	6.246%	$147.6076	$147.61	$147.60	$147.60
7 purchase totals =	$808.01		$870.9153	$870.91	$870.90	$870.80