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	$18.84	9.180%	$20.5695	$20.57	$20.55	$20.60
Purchase #2	$124.52	6.252%	$132.305	$132.31	$132.30	$132.30
Purchase #3	$196.91	3.799%	$204.3906	$204.39	$204.40	$204.40
Purchase #4	$169.70	9.415%	$185.6773	$185.68	$185.70	$185.70
Purchase #5	$70.47	10.112%	$77.5959	$77.60	$77.60	$77.60
Purchase #6	$129.71	13.164%	$146.785	$146.79	$146.80	$146.80
Purchase #7	$229.52	11.111%	$255.022	$255.02	$255.00	$255.00
7 purchase totals =	$939.67		$1,022.3453	$1,022.36	$1,022.35	$1,022.40