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	$139.36	8.779%	$151.5944	$151.59	$151.60	$151.60
Purchase #2	$240.39	12.799%	$271.1575	$271.16	$271.15	$271.20
Purchase #3	$141.44	4.805%	$148.2362	$148.24	$148.25	$148.20
Purchase #4	$47.42	12.635%	$53.4115	$53.41	$53.40	$53.40
Purchase #5	$27.84	6.211%	$29.5691	$29.57	$29.55	$29.60
Purchase #6	$80.58	11.253%	$89.6477	$89.65	$89.65	$89.60
Purchase #7	$57.48	3.594%	$59.5458	$59.55	$59.55	$59.50
7 purchase totals =	$734.51		$803.1622	$803.17	$803.15	$803.10