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	$20.96	3.469%	$21.6871	$21.69	$21.70	$21.70
Purchase #2	$118.37	4.142%	$123.2729	$123.27	$123.25	$123.30
Purchase #3	$13.79	4.168%	$14.3648	$14.36	$14.35	$14.40
Purchase #4	$250.63	10.662%	$277.3522	$277.35	$277.35	$277.40
Purchase #5	$21.73	4.741%	$22.7602	$22.76	$22.75	$22.80
Purchase #6	$49.26	10.242%	$54.3052	$54.31	$54.30	$54.30
Purchase #7	$88.59	4.845%	$92.8822	$92.88	$92.90	$92.90
7 purchase totals =	$563.33		$606.6246	$606.62	$606.60	$606.80