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	$92.61	12.187%	$103.8964	$103.90	$103.90	$103.90
Purchase #2	$173.97	4.518%	$181.83	$181.83	$181.85	$181.80
Purchase #3	$195.83	4.568%	$204.7755	$204.78	$204.80	$204.80
Purchase #4	$57.92	6.359%	$61.6031	$61.60	$61.60	$61.60
Purchase #5	$148.89	11.779%	$166.4278	$166.43	$166.45	$166.40
Purchase #6	$157.87	8.596%	$171.4405	$171.44	$171.45	$171.40
Purchase #7	$43.26	11.167%	$48.0908	$48.09	$48.10	$48.10
7 purchase totals =	$870.35		$938.0641	$938.07	$938.15	$938.00