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	$249.48	9.692%	$273.6596	$273.66	$273.65	$273.70
Purchase #2	$201.27	5.778%	$212.8994	$212.90	$212.90	$212.90
Purchase #3	$68.67	6.260%	$72.9687	$72.97	$72.95	$73.00
Purchase #4	$139.47	8.318%	$151.0711	$151.07	$151.05	$151.10
Purchase #5	$25.25	11.504%	$28.1548	$28.15	$28.15	$28.20
Purchase #6	$46.80	13.822%	$53.2687	$53.27	$53.25	$53.30
Purchase #7	$89.78	10.798%	$99.4744	$99.47	$99.45	$99.50
7 purchase totals =	$820.72		$891.4967	$891.49	$891.40	$891.70