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	$237.85	8.739%	$258.6357	$258.64	$258.65	$258.60
Purchase #2	$35.38	5.478%	$37.3181	$37.32	$37.30	$37.30
Purchase #3	$224.55	13.505%	$254.8755	$254.88	$254.90	$254.90
Purchase #4	$15.48	12.613%	$17.4325	$17.43	$17.45	$17.40
Purchase #5	$225.40	11.342%	$250.9649	$250.96	$250.95	$251.00
Purchase #6	$91.39	8.515%	$99.1719	$99.17	$99.15	$99.20
Purchase #7	$112.96	4.547%	$118.0963	$118.10	$118.10	$118.10
7 purchase totals =	$943.01		$1,036.4949	$1,036.50	$1,036.50	$1,036.50