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	$199.65	10.273%	$220.16	$220.16	$220.15	$220.20
Purchase #2	$56.83	10.158%	$62.6028	$62.60	$62.60	$62.60
Purchase #3	$19.39	7.731%	$20.889	$20.89	$20.90	$20.90
Purchase #4	$103.85	5.386%	$109.4434	$109.44	$109.45	$109.40
Purchase #5	$30.53	7.463%	$32.8085	$32.81	$32.80	$32.80
Purchase #6	$223.74	4.683%	$234.2177	$234.22	$234.20	$234.20
Purchase #7	$228.92	5.401%	$241.284	$241.28	$241.30	$241.30
7 purchase totals =	$862.91		$921.4054	$921.40	$921.40	$921.40