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	$90.95	11.398%	$101.3165	$101.32	$101.30	$101.30
Purchase #2	$39.80	7.388%	$42.7404	$42.74	$42.75	$42.70
Purchase #3	$90.62	3.266%	$93.5796	$93.58	$93.60	$93.60
Purchase #4	$24.47	4.334%	$25.5305	$25.53	$25.55	$25.50
Purchase #5	$100.95	8.794%	$109.8275	$109.83	$109.85	$109.80
Purchase #6	$88.91	10.727%	$98.4474	$98.45	$98.45	$98.40
Purchase #7	$77.43	3.401%	$80.0634	$80.06	$80.05	$80.10
7 purchase totals =	$513.13		$551.5053	$551.51	$551.55	$551.40