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	$60.54	12.110%	$67.8714	$67.87	$67.85	$67.90
Purchase #2	$108.94	13.524%	$123.673	$123.67	$123.65	$123.70
Purchase #3	$50.92	5.341%	$53.6396	$53.64	$53.65	$53.60
Purchase #4	$77.33	7.420%	$83.0679	$83.07	$83.05	$83.10
Purchase #5	$85.48	3.426%	$88.4085	$88.41	$88.40	$88.40
Purchase #6	$33.36	3.384%	$34.4889	$34.49	$34.50	$34.50
Purchase #7	$46.77	5.640%	$49.4078	$49.41	$49.40	$49.40
7 purchase totals =	$463.34		$500.5571	$500.56	$500.50	$500.60