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	$93.49	7.429%	$100.4354	$100.44	$100.45	$100.40
Purchase #2	$177.73	4.366%	$185.4897	$185.49	$185.50	$185.50
Purchase #3	$90.93	6.802%	$97.1151	$97.12	$97.10	$97.10
Purchase #4	$66.83	7.547%	$71.8737	$71.87	$71.85	$71.90
Purchase #5	$135.75	6.619%	$144.7353	$144.74	$144.75	$144.70
Purchase #6	$10.56	12.431%	$11.8727	$11.87	$11.85	$11.90
Purchase #7	$120.86	6.107%	$128.2409	$128.24	$128.25	$128.20
7 purchase totals =	$696.15		$739.7628	$739.77	$739.75	$739.70