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	$222.41	13.179%	$251.7214	$251.72	$251.70	$251.70
Purchase #2	$49.35	5.681%	$52.1536	$52.15	$52.15	$52.20
Purchase #3	$82.99	9.112%	$90.552	$90.55	$90.55	$90.60
Purchase #4	$82.92	13.306%	$93.9533	$93.95	$93.95	$94.00
Purchase #5	$223.87	7.670%	$241.0408	$241.04	$241.05	$241.00
Purchase #6	$49.25	8.563%	$53.4673	$53.47	$53.45	$53.50
Purchase #7	$43.72	3.540%	$45.2677	$45.27	$45.25	$45.30
7 purchase totals =	$754.51		$828.1561	$828.15	$828.10	$828.30