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	$122.40	9.584%	$134.1308	$134.13	$134.15	$134.10
Purchase #2	$142.77	7.266%	$153.1437	$153.14	$153.15	$153.10
Purchase #3	$147.88	11.185%	$164.4204	$164.42	$164.40	$164.40
Purchase #4	$19.87	10.187%	$21.8942	$21.89	$21.90	$21.90
Purchase #5	$50.57	8.845%	$55.0429	$55.04	$55.05	$55.00
Purchase #6	$210.83	8.302%	$228.3331	$228.33	$228.35	$228.30
Purchase #7	$42.72	7.379%	$45.8723	$45.87	$45.85	$45.90
7 purchase totals =	$737.04		$802.8374	$802.82	$802.85	$802.70