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	$236.48	12.862%	$266.8961	$266.90	$266.90	$266.90
Purchase #2	$226.90	10.452%	$250.6156	$250.62	$250.60	$250.60
Purchase #3	$117.56	11.604%	$131.2017	$131.20	$131.20	$131.20
Purchase #4	$19.83	9.613%	$21.7363	$21.74	$21.75	$21.70
Purchase #5	$142.25	4.230%	$148.2672	$148.27	$148.25	$148.30
Purchase #6	$245.84	13.434%	$278.8661	$278.87	$278.85	$278.90
Purchase #7	$147.73	6.173%	$156.8494	$156.85	$156.85	$156.80
7 purchase totals =	$1,136.59		$1,254.4324	$1,254.45	$1,254.40	$1,254.40