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	$61.42	7.738%	$66.1727	$66.17	$66.15	$66.20
Purchase #2	$27.57	3.381%	$28.5021	$28.50	$28.50	$28.50
Purchase #3	$99.87	4.660%	$104.5239	$104.52	$104.50	$104.50
Purchase #4	$109.43	10.408%	$120.8195	$120.82	$120.80	$120.80
Purchase #5	$210.98	5.842%	$223.3055	$223.31	$223.30	$223.30
Purchase #6	$223.66	13.790%	$254.5027	$254.50	$254.50	$254.50
Purchase #7	$158.27	3.637%	$164.0263	$164.03	$164.05	$164.00
7 purchase totals =	$891.20		$961.8527	$961.85	$961.80	$961.80