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	$138.45	12.250%	$155.4101	$155.41	$155.40	$155.40
Purchase #2	$231.77	9.807%	$254.4997	$254.50	$254.50	$254.50
Purchase #3	$171.48	8.409%	$185.8998	$185.90	$185.90	$185.90
Purchase #4	$50.51	11.773%	$56.4565	$56.46	$56.45	$56.50
Purchase #5	$131.27	4.147%	$136.7138	$136.71	$136.70	$136.70
Purchase #6	$248.76	9.676%	$272.83	$272.83	$272.85	$272.80
Purchase #7	$22.74	10.324%	$25.0877	$25.09	$25.10	$25.10
7 purchase totals =	$994.98		$1,086.8976	$1,086.90	$1,086.90	$1,086.90