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	$159.39	12.675%	$179.5927	$179.59	$179.60	$179.60
Purchase #2	$41.67	9.230%	$45.5161	$45.52	$45.50	$45.50
Purchase #3	$22.42	13.705%	$25.4927	$25.49	$25.50	$25.50
Purchase #4	$158.53	10.309%	$174.8729	$174.87	$174.85	$174.90
Purchase #5	$148.74	9.504%	$162.8762	$162.88	$162.90	$162.90
Purchase #6	$195.64	5.177%	$205.7683	$205.77	$205.75	$205.80
Purchase #7	$176.82	4.348%	$184.5081	$184.51	$184.50	$184.50
7 purchase totals =	$903.21		$978.6270	$978.63	$978.60	$978.70