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	$171.31	10.404%	$189.1331	$189.13	$189.15	$189.10
Purchase #2	$123.27	8.440%	$133.674	$133.67	$133.65	$133.70
Purchase #3	$70.86	12.318%	$79.5885	$79.59	$79.60	$79.60
Purchase #4	$167.47	3.119%	$172.6934	$172.69	$172.70	$172.70
Purchase #5	$75.37	4.175%	$78.5167	$78.52	$78.50	$78.50
Purchase #6	$108.38	7.366%	$116.3633	$116.36	$116.35	$116.40
Purchase #7	$211.76	11.266%	$235.6169	$235.62	$235.60	$235.60
7 purchase totals =	$928.42		$1,005.5859	$1,005.58	$1,005.55	$1,005.60