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	$178.42	4.323%	$186.1331	$186.13	$186.15	$186.10
Purchase #2	$73.89	11.739%	$82.5639	$82.56	$82.55	$82.60
Purchase #3	$20.87	8.838%	$22.7145	$22.71	$22.70	$22.70
Purchase #4	$204.94	10.294%	$226.0365	$226.04	$226.05	$226.00
Purchase #5	$146.56	9.807%	$160.9331	$160.93	$160.95	$160.90
Purchase #6	$223.80	4.464%	$233.7904	$233.79	$233.80	$233.80
Purchase #7	$114.51	11.377%	$127.5378	$127.54	$127.55	$127.50
7 purchase totals =	$962.99		$1,039.7093	$1,039.70	$1,039.75	$1,039.60