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	$117.91	11.464%	$131.4272	$131.43	$131.45	$131.40
Purchase #2	$176.39	13.111%	$199.5165	$199.52	$199.50	$199.50
Purchase #3	$78.52	3.647%	$81.3836	$81.38	$81.40	$81.40
Purchase #4	$19.71	7.491%	$21.1865	$21.19	$21.20	$21.20
Purchase #5	$233.84	6.383%	$248.766	$248.77	$248.75	$248.80
Purchase #6	$105.63	12.533%	$118.8686	$118.87	$118.85	$118.90
Purchase #7	$94.40	5.232%	$99.339	$99.34	$99.35	$99.30
7 purchase totals =	$826.40		$900.4874	$900.50	$900.50	$900.50