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	$37.91	3.616%	$39.2808	$39.28	$39.30	$39.30
Purchase #2	$138.65	8.557%	$150.5143	$150.51	$150.50	$150.50
Purchase #3	$236.89	13.455%	$268.7635	$268.76	$268.75	$268.80
Purchase #4	$149.72	3.454%	$154.8913	$154.89	$154.90	$154.90
Purchase #5	$36.95	8.773%	$40.1916	$40.19	$40.20	$40.20
Purchase #6	$57.28	5.665%	$60.5249	$60.52	$60.50	$60.50
Purchase #7	$242.46	4.613%	$253.6447	$253.64	$253.65	$253.60
7 purchase totals =	$899.86		$967.8111	$967.79	$967.80	$967.80