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	$37.93	5.574%	$40.0442	$40.04	$40.05	$40.00
Purchase #2	$123.27	3.166%	$127.1727	$127.17	$127.15	$127.20
Purchase #3	$35.51	6.441%	$37.7972	$37.80	$37.80	$37.80
Purchase #4	$118.41	10.486%	$130.8265	$130.83	$130.85	$130.80
Purchase #5	$208.36	7.220%	$223.4036	$223.40	$223.40	$223.40
Purchase #6	$152.95	6.693%	$163.1869	$163.19	$163.20	$163.20
Purchase #7	$124.47	4.539%	$130.1197	$130.12	$130.10	$130.10
7 purchase totals =	$800.90		$852.5508	$852.55	$852.55	$852.50