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	$170.83	10.142%	$188.1556	$188.16	$188.15	$188.20
Purchase #2	$5.37	11.278%	$5.9756	$5.98	$6.00	$6.00
Purchase #3	$217.90	13.622%	$247.5823	$247.58	$247.60	$247.60
Purchase #4	$76.28	5.581%	$80.5372	$80.54	$80.55	$80.50
Purchase #5	$34.92	12.152%	$39.1635	$39.16	$39.15	$39.20
Purchase #6	$127.74	11.767%	$142.7712	$142.77	$142.75	$142.80
Purchase #7	$147.39	6.366%	$156.7728	$156.77	$156.75	$156.80
7 purchase totals =	$780.43		$860.9582	$860.96	$860.95	$861.10