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	$225.71	3.491%	$233.5895	$233.59	$233.60	$233.60
Purchase #2	$40.93	11.187%	$45.5088	$45.51	$45.50	$45.50
Purchase #3	$225.90	6.612%	$240.8365	$240.84	$240.85	$240.80
Purchase #4	$215.51	7.513%	$231.7013	$231.70	$231.70	$231.70
Purchase #5	$14.65	7.581%	$15.7606	$15.76	$15.75	$15.80
Purchase #6	$49.50	9.238%	$54.0728	$54.07	$54.05	$54.10
Purchase #7	$96.74	5.321%	$101.8875	$101.89	$101.90	$101.90
7 purchase totals =	$868.94		$923.3570	$923.36	$923.35	$923.40