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	$118.72	10.314%	$130.9648	$130.96	$130.95	$131.00
Purchase #2	$57.90	4.441%	$60.4713	$60.47	$60.45	$60.50
Purchase #3	$76.50	7.595%	$82.3102	$82.31	$82.30	$82.30
Purchase #4	$131.26	9.561%	$143.8098	$143.81	$143.80	$143.80
Purchase #5	$138.29	7.554%	$148.7364	$148.74	$148.75	$148.70
Purchase #6	$190.33	4.776%	$199.4202	$199.42	$199.40	$199.40
Purchase #7	$130.31	12.496%	$146.5935	$146.59	$146.60	$146.60
7 purchase totals =	$843.31		$912.3062	$912.30	$912.25	$912.30