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	$42.91	3.646%	$44.4745	$44.47	$44.45	$44.50
Purchase #2	$48.51	11.823%	$54.2453	$54.25	$54.25	$54.20
Purchase #3	$42.36	9.787%	$46.5058	$46.51	$46.50	$46.50
Purchase #4	$57.37	7.114%	$61.4513	$61.45	$61.45	$61.50
Purchase #5	$176.65	10.749%	$195.6381	$195.64	$195.65	$195.60
Purchase #6	$179.39	6.771%	$191.5365	$191.54	$191.55	$191.50
Purchase #7	$226.42	9.285%	$247.4431	$247.44	$247.45	$247.40
7 purchase totals =	$773.61		$841.2946	$841.30	$841.30	$841.20