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	$170.91	4.754%	$179.0351	$179.04	$179.05	$179.00
Purchase #2	$212.87	11.860%	$238.1164	$238.12	$238.10	$238.10
Purchase #3	$42.51	7.264%	$45.5979	$45.60	$45.60	$45.60
Purchase #4	$175.82	8.223%	$190.2777	$190.28	$190.30	$190.30
Purchase #5	$127.25	11.621%	$142.0377	$142.04	$142.05	$142.00
Purchase #6	$96.57	12.307%	$108.4549	$108.45	$108.45	$108.50
Purchase #7	$58.31	5.541%	$61.541	$61.54	$61.55	$61.50
7 purchase totals =	$884.24		$965.0607	$965.07	$965.10	$965.00