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	$91.73	11.531%	$102.3074	$102.31	$102.30	$102.30
Purchase #2	$144.86	9.252%	$158.2624	$158.26	$158.25	$158.30
Purchase #3	$32.71	6.161%	$34.7253	$34.73	$34.75	$34.70
Purchase #4	$128.66	12.165%	$144.3115	$144.31	$144.30	$144.30
Purchase #5	$179.27	4.735%	$187.7584	$187.76	$187.75	$187.80
Purchase #6	$56.88	7.714%	$61.2677	$61.27	$61.25	$61.30
Purchase #7	$207.48	7.821%	$223.707	$223.71	$223.70	$223.70
7 purchase totals =	$841.59		$912.3397	$912.35	$912.30	$912.40