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	$240.64	10.530%	$265.9794	$265.98	$266.00	$266.00
Purchase #2	$137.77	12.706%	$155.2751	$155.28	$155.30	$155.30
Purchase #3	$77.26	6.333%	$82.1529	$82.15	$82.15	$82.20
Purchase #4	$158.66	8.222%	$171.705	$171.71	$171.70	$171.70
Purchase #5	$206.45	11.191%	$229.5538	$229.55	$229.55	$229.60
Purchase #6	$128.67	10.596%	$142.3039	$142.30	$142.30	$142.30
Purchase #7	$39.50	6.720%	$42.1544	$42.15	$42.15	$42.20
7 purchase totals =	$988.95		$1,089.1245	$1,089.12	$1,089.15	$1,089.30