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	$34.46	9.842%	$37.8516	$37.85	$37.85	$37.90
Purchase #2	$69.94	6.648%	$74.5896	$74.59	$74.60	$74.60
Purchase #3	$50.34	5.855%	$53.2874	$53.29	$53.30	$53.30
Purchase #4	$151.25	5.145%	$159.0318	$159.03	$159.05	$159.00
Purchase #5	$35.99	11.441%	$40.1076	$40.11	$40.10	$40.10
Purchase #6	$46.69	11.103%	$51.874	$51.87	$51.85	$51.90
Purchase #7	$72.71	8.166%	$78.6475	$78.65	$78.65	$78.60
7 purchase totals =	$461.38		$495.3895	$495.39	$495.40	$495.40