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	$207.87	6.246%	$220.8536	$220.85	$220.85	$220.90
Purchase #2	$173.97	10.668%	$192.5291	$192.53	$192.55	$192.50
Purchase #3	$166.89	11.325%	$185.7903	$185.79	$185.80	$185.80
Purchase #4	$122.57	12.853%	$138.3239	$138.32	$138.30	$138.30
Purchase #5	$235.69	8.520%	$255.7708	$255.77	$255.75	$255.80
Purchase #6	$95.65	10.732%	$105.9152	$105.92	$105.90	$105.90
Purchase #7	$181.89	9.502%	$199.1732	$199.17	$199.15	$199.20
7 purchase totals =	$1,184.53		$1,298.3561	$1,298.35	$1,298.30	$1,298.40