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	$84.83	6.766%	$90.5696	$90.57	$90.55	$90.60
Purchase #2	$21.94	13.520%	$24.9063	$24.91	$24.90	$24.90
Purchase #3	$59.49	13.117%	$67.2933	$67.29	$67.30	$67.30
Purchase #4	$16.67	3.490%	$17.2518	$17.25	$17.25	$17.30
Purchase #5	$30.55	9.334%	$33.4015	$33.40	$33.40	$33.40
Purchase #6	$130.53	10.214%	$143.8623	$143.86	$143.85	$143.90
Purchase #7	$135.47	11.303%	$150.7822	$150.78	$150.80	$150.80
7 purchase totals =	$479.48		$528.0670	$528.06	$528.05	$528.20