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	$139.36	3.464%	$144.1874	$144.19	$144.20	$144.20
Purchase #2	$53.31	8.347%	$57.7598	$57.76	$57.75	$57.80
Purchase #3	$67.67	13.863%	$77.0511	$77.05	$77.05	$77.10
Purchase #4	$250.60	11.667%	$279.8375	$279.84	$279.85	$279.80
Purchase #5	$169.92	13.142%	$192.2509	$192.25	$192.25	$192.30
Purchase #6	$89.99	9.373%	$98.4248	$98.42	$98.40	$98.40
Purchase #7	$151.46	9.292%	$165.5337	$165.53	$165.55	$165.50
7 purchase totals =	$922.31		$1,015.0452	$1,015.04	$1,015.05	$1,015.10