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	$139.87	13.238%	$158.386	$158.39	$158.40	$158.40
Purchase #2	$89.41	7.718%	$96.3107	$96.31	$96.30	$96.30
Purchase #3	$92.87	7.858%	$100.1677	$100.17	$100.15	$100.20
Purchase #4	$57.28	8.855%	$62.3521	$62.35	$62.35	$62.40
Purchase #5	$210.32	8.367%	$227.9175	$227.92	$227.90	$227.90
Purchase #6	$157.91	11.149%	$175.5154	$175.52	$175.50	$175.50
Purchase #7	$197.55	12.723%	$222.6843	$222.68	$222.70	$222.70
7 purchase totals =	$945.21		$1,043.3337	$1,043.34	$1,043.30	$1,043.40