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	$166.26	3.624%	$172.2853	$172.29	$172.30	$172.30
Purchase #2	$247.26	9.802%	$271.4964	$271.50	$271.50	$271.50
Purchase #3	$225.44	3.167%	$232.5797	$232.58	$232.60	$232.60
Purchase #4	$170.27	9.188%	$185.9144	$185.91	$185.90	$185.90
Purchase #5	$137.67	5.659%	$145.4607	$145.46	$145.45	$145.50
Purchase #6	$38.46	11.184%	$42.7614	$42.76	$42.75	$42.80
Purchase #7	$5.62	8.773%	$6.113	$6.11	$6.10	$6.10
7 purchase totals =	$990.98		$1,056.6109	$1,056.61	$1,056.60	$1,056.70