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	$130.88	11.693%	$146.1838	$146.18	$146.20	$146.20
Purchase #2	$62.42	5.437%	$65.8138	$65.81	$65.80	$65.80
Purchase #3	$123.58	10.630%	$136.7166	$136.72	$136.70	$136.70
Purchase #4	$28.61	5.570%	$30.2036	$30.20	$30.20	$30.20
Purchase #5	$111.43	5.394%	$117.4405	$117.44	$117.45	$117.40
Purchase #6	$139.89	3.460%	$144.7302	$144.73	$144.75	$144.70
Purchase #7	$150.72	11.723%	$168.3889	$168.39	$168.40	$168.40
7 purchase totals =	$747.53		$809.4774	$809.47	$809.50	$809.40