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	$136.47	13.722%	$155.1964	$155.20	$155.20	$155.20
Purchase #2	$146.41	8.176%	$158.3805	$158.38	$158.40	$158.40
Purchase #3	$53.85	10.532%	$59.5215	$59.52	$59.50	$59.50
Purchase #4	$120.70	13.121%	$136.537	$136.54	$136.55	$136.50
Purchase #5	$82.55	10.613%	$91.311	$91.31	$91.30	$91.30
Purchase #6	$181.79	8.591%	$197.4076	$197.41	$197.40	$197.40
Purchase #7	$62.39	5.181%	$65.6224	$65.62	$65.60	$65.60
7 purchase totals =	$784.16		$863.9764	$863.98	$863.95	$863.90