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	$91.45	6.683%	$97.5616	$97.56	$97.55	$97.60
Purchase #2	$63.38	7.104%	$67.8825	$67.88	$67.90	$67.90
Purchase #3	$172.34	13.437%	$195.4973	$195.50	$195.50	$195.50
Purchase #4	$157.52	13.588%	$178.9238	$178.92	$178.90	$178.90
Purchase #5	$137.60	4.123%	$143.2732	$143.27	$143.25	$143.30
Purchase #6	$45.77	4.402%	$47.7848	$47.78	$47.80	$47.80
Purchase #7	$79.46	11.197%	$88.3571	$88.36	$88.35	$88.40
7 purchase totals =	$747.52		$819.2803	$819.27	$819.25	$819.40