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	$230.64	3.432%	$238.5556	$238.56	$238.55	$238.60
Purchase #2	$128.80	6.466%	$137.1282	$137.13	$137.15	$137.10
Purchase #3	$55.65	4.173%	$57.9723	$57.97	$57.95	$58.00
Purchase #4	$87.87	3.314%	$90.782	$90.78	$90.80	$90.80
Purchase #5	$227.58	8.687%	$247.3499	$247.35	$247.35	$247.30
Purchase #6	$24.25	13.102%	$27.4272	$27.43	$27.45	$27.40
Purchase #7	$91.57	8.362%	$99.2271	$99.23	$99.25	$99.20
7 purchase totals =	$846.36		$898.4423	$898.45	$898.50	$898.40