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	$37.87	3.606%	$39.2356	$39.24	$39.25	$39.20
Purchase #2	$11.56	8.205%	$12.5085	$12.51	$12.50	$12.50
Purchase #3	$197.76	8.772%	$215.1075	$215.11	$215.10	$215.10
Purchase #4	$107.90	3.466%	$111.6398	$111.64	$111.65	$111.60
Purchase #5	$100.26	5.253%	$105.5267	$105.53	$105.55	$105.50
Purchase #6	$250.59	9.488%	$274.366	$274.37	$274.35	$274.40
Purchase #7	$47.47	11.667%	$53.0083	$53.01	$53.00	$53.00
7 purchase totals =	$753.41		$811.3924	$811.41	$811.40	$811.30