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	$35.94	5.466%	$37.9045	$37.90	$37.90	$37.90
Purchase #2	$149.72	3.254%	$154.5919	$154.59	$154.60	$154.60
Purchase #3	$90.54	4.483%	$94.5989	$94.60	$94.60	$94.60
Purchase #4	$21.77	7.761%	$23.4596	$23.46	$23.45	$23.50
Purchase #5	$186.57	11.847%	$208.6729	$208.67	$208.65	$208.70
Purchase #6	$197.89	6.394%	$210.5431	$210.54	$210.55	$210.50
Purchase #7	$148.88	3.685%	$154.3662	$154.37	$154.35	$154.40
7 purchase totals =	$831.31		$884.1371	$884.13	$884.10	$884.20