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	$128.92	3.303%	$133.1782	$133.18	$133.20	$133.20
Purchase #2	$151.34	3.298%	$156.3312	$156.33	$156.35	$156.30
Purchase #3	$42.78	12.436%	$48.1001	$48.10	$48.10	$48.10
Purchase #4	$13.57	3.867%	$14.0948	$14.09	$14.10	$14.10
Purchase #5	$103.63	8.584%	$112.5256	$112.53	$112.55	$112.50
Purchase #6	$244.52	13.184%	$276.7575	$276.76	$276.75	$276.80
Purchase #7	$94.46	6.510%	$100.6093	$100.61	$100.60	$100.60
7 purchase totals =	$779.22		$841.5967	$841.60	$841.65	$841.60