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	$175.83	13.400%	$199.3912	$199.39	$199.40	$199.40
Purchase #2	$135.92	10.697%	$150.4594	$150.46	$150.45	$150.50
Purchase #3	$93.69	8.612%	$101.7586	$101.76	$101.75	$101.80
Purchase #4	$94.66	11.500%	$105.5459	$105.55	$105.55	$105.50
Purchase #5	$87.70	12.452%	$98.6204	$98.62	$98.60	$98.60
Purchase #6	$50.27	4.553%	$52.5588	$52.56	$52.55	$52.60
Purchase #7	$46.82	4.290%	$48.8286	$48.83	$48.85	$48.80
7 purchase totals =	$684.89		$757.1629	$757.17	$757.15	$757.20