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	$249.93	3.451%	$258.5551	$258.56	$258.55	$258.60
Purchase #2	$84.51	11.313%	$94.0706	$94.07	$94.05	$94.10
Purchase #3	$207.50	7.217%	$222.4753	$222.48	$222.50	$222.50
Purchase #4	$75.30	9.518%	$82.4671	$82.47	$82.45	$82.50
Purchase #5	$51.25	4.840%	$53.7305	$53.73	$53.75	$53.70
Purchase #6	$110.47	10.168%	$121.7026	$121.70	$121.70	$121.70
Purchase #7	$160.82	7.307%	$172.5711	$172.57	$172.55	$172.60
7 purchase totals =	$939.78		$1,005.5723	$1,005.58	$1,005.55	$1,005.70