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	$12.43	11.856%	$13.9037	$13.90	$13.90	$13.90
Purchase #2	$157.70	11.374%	$175.6368	$175.64	$175.65	$175.60
Purchase #3	$216.73	5.863%	$229.4369	$229.44	$229.45	$229.40
Purchase #4	$56.98	7.662%	$61.3458	$61.35	$61.35	$61.30
Purchase #5	$224.32	9.227%	$245.018	$245.02	$245.00	$245.00
Purchase #6	$220.31	11.130%	$244.8305	$244.83	$244.85	$244.80
Purchase #7	$151.78	13.718%	$172.6012	$172.60	$172.60	$172.60
7 purchase totals =	$1,040.25		$1,142.7729	$1,142.78	$1,142.80	$1,142.60