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	$238.97	13.684%	$271.6707	$271.67	$271.65	$271.70
Purchase #2	$17.97	4.128%	$18.7118	$18.71	$18.70	$18.70
Purchase #3	$133.71	8.284%	$144.7865	$144.79	$144.80	$144.80
Purchase #4	$74.30	11.492%	$82.8386	$82.84	$82.85	$82.80
Purchase #5	$129.63	11.867%	$145.0132	$145.01	$145.00	$145.00
Purchase #6	$216.51	5.103%	$227.5585	$227.56	$227.55	$227.60
Purchase #7	$86.86	4.457%	$90.7314	$90.73	$90.75	$90.70
7 purchase totals =	$897.95		$981.3107	$981.31	$981.30	$981.30