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	$151.55	13.708%	$172.3245	$172.32	$172.30	$172.30
Purchase #2	$179.92	5.618%	$190.0279	$190.03	$190.05	$190.00
Purchase #3	$169.90	12.700%	$191.4773	$191.48	$191.50	$191.50
Purchase #4	$10.47	10.282%	$11.5465	$11.55	$11.55	$11.50
Purchase #5	$54.46	7.338%	$58.4563	$58.46	$58.45	$58.50
Purchase #6	$128.52	3.731%	$133.3151	$133.32	$133.30	$133.30
Purchase #7	$139.66	3.853%	$145.0411	$145.04	$145.05	$145.00
7 purchase totals =	$834.48		$902.1887	$902.20	$902.20	$902.10