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	$137.50	8.222%	$148.8053	$148.81	$148.80	$148.80
Purchase #2	$180.75	10.334%	$199.4287	$199.43	$199.45	$199.40
Purchase #3	$183.45	5.688%	$193.8846	$193.88	$193.90	$193.90
Purchase #4	$84.86	5.603%	$89.6147	$89.61	$89.60	$89.60
Purchase #5	$138.33	9.779%	$151.8573	$151.86	$151.85	$151.90
Purchase #6	$116.92	10.162%	$128.8014	$128.80	$128.80	$128.80
Purchase #7	$161.66	4.797%	$169.4148	$169.41	$169.40	$169.40
7 purchase totals =	$1,003.47		$1,081.8068	$1,081.80	$1,081.80	$1,081.80