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	$16.38	10.786%	$18.1467	$18.15	$18.15	$18.10
Purchase #2	$162.89	5.798%	$172.3344	$172.33	$172.35	$172.30
Purchase #3	$68.28	8.134%	$73.8339	$73.83	$73.85	$73.80
Purchase #4	$101.58	7.257%	$108.9517	$108.95	$108.95	$109.00
Purchase #5	$195.82	8.842%	$213.1344	$213.13	$213.15	$213.10
Purchase #6	$113.37	12.654%	$127.7158	$127.72	$127.70	$127.70
Purchase #7	$183.96	4.341%	$191.9457	$191.95	$191.95	$191.90
7 purchase totals =	$842.28		$906.0626	$906.06	$906.10	$905.90