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	$76.89	3.265%	$79.4005	$79.40	$79.40	$79.40
Purchase #2	$172.57	6.753%	$184.2237	$184.22	$184.20	$184.20
Purchase #3	$88.45	13.399%	$100.3014	$100.30	$100.30	$100.30
Purchase #4	$42.74	5.653%	$45.1561	$45.16	$45.15	$45.20
Purchase #5	$175.69	9.412%	$192.2259	$192.23	$192.25	$192.20
Purchase #6	$111.45	6.129%	$118.2808	$118.28	$118.30	$118.30
Purchase #7	$82.61	9.497%	$90.4555	$90.46	$90.45	$90.50
7 purchase totals =	$750.40		$810.0439	$810.05	$810.05	$810.10