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	$249.49	3.289%	$257.6957	$257.70	$257.70	$257.70
Purchase #2	$57.30	4.312%	$59.7708	$59.77	$59.75	$59.80
Purchase #3	$55.46	10.213%	$61.1241	$61.12	$61.10	$61.10
Purchase #4	$176.66	10.648%	$195.4708	$195.47	$195.45	$195.50
Purchase #5	$114.61	7.713%	$123.4499	$123.45	$123.45	$123.40
Purchase #6	$157.51	6.559%	$167.8411	$167.84	$167.85	$167.80
Purchase #7	$84.34	9.271%	$92.1592	$92.16	$92.15	$92.20
7 purchase totals =	$895.37		$957.5116	$957.51	$957.45	$957.50