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	$30.98	6.229%	$32.9097	$32.91	$32.90	$32.90
Purchase #2	$48.89	7.420%	$52.5176	$52.52	$52.50	$52.50
Purchase #3	$131.61	13.657%	$149.584	$149.58	$149.60	$149.60
Purchase #4	$82.89	7.479%	$89.0893	$89.09	$89.10	$89.10
Purchase #5	$222.28	7.728%	$239.4578	$239.46	$239.45	$239.50
Purchase #6	$64.57	6.698%	$68.8949	$68.89	$68.90	$68.90
Purchase #7	$12.74	11.682%	$14.2283	$14.23	$14.25	$14.20
7 purchase totals =	$593.96		$646.6816	$646.68	$646.70	$646.70