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	$242.95	12.188%	$272.5607	$272.56	$272.55	$272.60
Purchase #2	$35.50	6.700%	$37.8785	$37.88	$37.90	$37.90
Purchase #3	$48.30	3.586%	$50.032	$50.03	$50.05	$50.00
Purchase #4	$83.72	6.388%	$89.068	$89.07	$89.05	$89.10
Purchase #5	$110.92	4.658%	$116.0867	$116.09	$116.10	$116.10
Purchase #6	$231.69	10.390%	$255.7626	$255.76	$255.75	$255.80
Purchase #7	$93.66	7.689%	$100.8615	$100.86	$100.85	$100.90
7 purchase totals =	$846.74		$922.2500	$922.25	$922.25	$922.40