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	$86.58	6.122%	$91.8804	$91.88	$91.90	$91.90
Purchase #2	$73.93	4.524%	$77.2746	$77.27	$77.25	$77.30
Purchase #3	$50.44	12.569%	$56.7798	$56.78	$56.80	$56.80
Purchase #4	$230.76	13.390%	$261.6588	$261.66	$261.65	$261.70
Purchase #5	$145.69	10.182%	$160.5242	$160.52	$160.50	$160.50
Purchase #6	$193.61	10.811%	$214.5412	$214.54	$214.55	$214.50
Purchase #7	$38.75	10.728%	$42.9071	$42.91	$42.90	$42.90
7 purchase totals =	$819.76		$905.5661	$905.56	$905.55	$905.60