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	$82.42	10.354%	$90.9538	$90.95	$90.95	$91.00
Purchase #2	$100.45	8.291%	$108.7783	$108.78	$108.80	$108.80
Purchase #3	$142.75	11.329%	$158.9221	$158.92	$158.90	$158.90
Purchase #4	$65.45	11.615%	$73.052	$73.05	$73.05	$73.10
Purchase #5	$249.74	11.366%	$278.1254	$278.13	$278.15	$278.10
Purchase #6	$167.51	6.583%	$178.5372	$178.54	$178.55	$178.50
Purchase #7	$152.86	13.115%	$172.9076	$172.91	$172.90	$172.90
7 purchase totals =	$961.18		$1,061.2764	$1,061.28	$1,061.30	$1,061.30