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	$49.55	11.793%	$55.3934	$55.39	$55.40	$55.40
Purchase #2	$129.86	11.436%	$144.7108	$144.71	$144.70	$144.70
Purchase #3	$151.78	13.798%	$172.7226	$172.72	$172.70	$172.70
Purchase #4	$69.27	4.130%	$72.1309	$72.13	$72.15	$72.10
Purchase #5	$175.78	6.139%	$186.5711	$186.57	$186.55	$186.60
Purchase #6	$227.58	3.662%	$235.914	$235.91	$235.90	$235.90
Purchase #7	$13.31	13.723%	$15.1365	$15.14	$15.15	$15.10
7 purchase totals =	$817.13		$882.5793	$882.57	$882.55	$882.50