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	$79.47	3.720%	$82.4263	$82.43	$82.45	$82.40
Purchase #2	$37.82	12.567%	$42.5728	$42.57	$42.55	$42.60
Purchase #3	$15.54	12.807%	$17.5302	$17.53	$17.55	$17.50
Purchase #4	$42.32	9.439%	$46.3146	$46.31	$46.30	$46.30
Purchase #5	$216.79	8.662%	$235.5683	$235.57	$235.55	$235.60
Purchase #6	$184.91	11.479%	$206.1358	$206.14	$206.15	$206.10
Purchase #7	$40.34	12.240%	$45.2776	$45.28	$45.30	$45.30
7 purchase totals =	$617.19		$675.8256	$675.83	$675.85	$675.80