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	$83.63	8.534%	$90.767	$90.77	$90.75	$90.80
Purchase #2	$36.95	7.731%	$39.8066	$39.81	$39.80	$39.80
Purchase #3	$15.84	12.479%	$17.8167	$17.82	$17.80	$17.80
Purchase #4	$94.38	6.812%	$100.8092	$100.81	$100.80	$100.80
Purchase #5	$127.29	5.843%	$134.7276	$134.73	$134.75	$134.70
Purchase #6	$34.45	8.218%	$37.2811	$37.28	$37.30	$37.30
Purchase #7	$54.27	4.201%	$56.5499	$56.55	$56.55	$56.50
7 purchase totals =	$446.81		$477.7581	$477.77	$477.75	$477.70