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	$21.56	7.825%	$23.2471	$23.25	$23.25	$23.20
Purchase #2	$46.35	4.404%	$48.3913	$48.39	$48.40	$48.40
Purchase #3	$167.40	3.640%	$173.4934	$173.49	$173.50	$173.50
Purchase #4	$230.26	11.385%	$256.4751	$256.48	$256.50	$256.50
Purchase #5	$55.77	7.538%	$59.9739	$59.97	$59.95	$60.00
Purchase #6	$20.51	6.142%	$21.7697	$21.77	$21.75	$21.80
Purchase #7	$144.50	5.387%	$152.2842	$152.28	$152.30	$152.30
7 purchase totals =	$686.35		$735.6347	$735.63	$735.65	$735.70