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	$165.55	8.506%	$179.6317	$179.63	$179.65	$179.60
Purchase #2	$247.76	3.239%	$255.7849	$255.78	$255.80	$255.80
Purchase #3	$205.65	7.524%	$221.1231	$221.12	$221.10	$221.10
Purchase #4	$104.48	11.762%	$116.7689	$116.77	$116.75	$116.80
Purchase #5	$40.80	4.205%	$42.5156	$42.52	$42.50	$42.50
Purchase #6	$104.52	4.397%	$109.1157	$109.12	$109.10	$109.10
Purchase #7	$59.85	10.777%	$66.3	$66.30	$66.30	$66.30
7 purchase totals =	$928.61		$991.2399	$991.24	$991.20	$991.20