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	$180.25	3.134%	$185.899	$185.90	$185.90	$185.90
Purchase #2	$58.46	5.680%	$61.7805	$61.78	$61.80	$61.80
Purchase #3	$93.92	5.486%	$99.0725	$99.07	$99.05	$99.10
Purchase #4	$249.70	10.434%	$275.7537	$275.75	$275.75	$275.80
Purchase #5	$116.66	11.318%	$129.8636	$129.86	$129.85	$129.90
Purchase #6	$119.31	9.501%	$130.6456	$130.65	$130.65	$130.60
Purchase #7	$33.27	6.436%	$35.4113	$35.41	$35.40	$35.40
7 purchase totals =	$851.57		$918.4262	$918.42	$918.40	$918.50