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	$113.26	11.705%	$126.5171	$126.52	$126.50	$126.50
Purchase #2	$105.30	13.504%	$119.5197	$119.52	$119.50	$119.50
Purchase #3	$82.95	9.743%	$91.0318	$91.03	$91.05	$91.00
Purchase #4	$154.74	13.667%	$175.8883	$175.89	$175.90	$175.90
Purchase #5	$88.33	3.209%	$91.1645	$91.16	$91.15	$91.20
Purchase #6	$160.78	5.842%	$170.1728	$170.17	$170.15	$170.20
Purchase #7	$116.65	8.275%	$126.3028	$126.30	$126.30	$126.30
7 purchase totals =	$822.01		$900.5970	$900.59	$900.55	$900.60