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	$114.41	5.341%	$120.5206	$120.52	$120.50	$120.50
Purchase #2	$36.76	10.744%	$40.7095	$40.71	$40.70	$40.70
Purchase #3	$135.80	11.853%	$151.8964	$151.90	$151.90	$151.90
Purchase #4	$17.82	13.455%	$20.2177	$20.22	$20.20	$20.20
Purchase #5	$68.46	11.726%	$76.4876	$76.49	$76.50	$76.50
Purchase #6	$247.30	5.162%	$260.0656	$260.07	$260.05	$260.10
Purchase #7	$115.65	6.758%	$123.4656	$123.47	$123.45	$123.50
7 purchase totals =	$736.20		$793.3630	$793.38	$793.30	$793.40