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	$28.43	13.120%	$32.16	$32.16	$32.15	$32.20
Purchase #2	$81.74	3.103%	$84.2764	$84.28	$84.30	$84.30
Purchase #3	$60.84	9.758%	$66.7768	$66.78	$66.80	$66.80
Purchase #4	$129.53	12.294%	$145.4544	$145.45	$145.45	$145.50
Purchase #5	$94.82	10.206%	$104.4973	$104.50	$104.50	$104.50
Purchase #6	$156.30	10.612%	$172.8866	$172.89	$172.90	$172.90
Purchase #7	$168.42	6.607%	$179.5475	$179.55	$179.55	$179.50
7 purchase totals =	$720.08		$785.5990	$785.61	$785.65	$785.70