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	$171.74	10.342%	$189.5014	$189.50	$189.50	$189.50
Purchase #2	$177.46	7.427%	$190.64	$190.64	$190.65	$190.60
Purchase #3	$141.55	9.690%	$155.2662	$155.27	$155.25	$155.30
Purchase #4	$69.76	10.152%	$76.842	$76.84	$76.85	$76.80
Purchase #5	$10.74	13.266%	$12.1648	$12.16	$12.15	$12.20
Purchase #6	$133.38	6.670%	$142.2764	$142.28	$142.30	$142.30
Purchase #7	$116.94	10.158%	$128.8188	$128.82	$128.80	$128.80
7 purchase totals =	$821.57		$895.5096	$895.51	$895.50	$895.50