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	$170.72	6.308%	$181.489	$181.49	$181.50	$181.50
Purchase #2	$180.81	3.715%	$187.5271	$187.53	$187.55	$187.50
Purchase #3	$220.64	7.250%	$236.6364	$236.64	$236.65	$236.60
Purchase #4	$159.34	12.233%	$178.8321	$178.83	$178.85	$178.80
Purchase #5	$66.57	9.158%	$72.6665	$72.67	$72.65	$72.70
Purchase #6	$60.26	11.685%	$67.3014	$67.30	$67.30	$67.30
Purchase #7	$204.45	6.659%	$218.0643	$218.06	$218.05	$218.10
7 purchase totals =	$1,062.79		$1,142.5168	$1,142.52	$1,142.55	$1,142.50