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	$238.89	11.586%	$266.5678	$266.57	$266.55	$266.60
Purchase #2	$58.55	13.507%	$66.4583	$66.46	$66.45	$66.50
Purchase #3	$172.37	3.552%	$178.4926	$178.49	$178.50	$178.50
Purchase #4	$35.47	6.793%	$37.8795	$37.88	$37.90	$37.90
Purchase #5	$74.72	10.118%	$82.2802	$82.28	$82.30	$82.30
Purchase #6	$173.69	5.339%	$182.9633	$182.96	$182.95	$183.00
Purchase #7	$163.74	6.653%	$174.6336	$174.63	$174.65	$174.60
7 purchase totals =	$917.43		$989.2753	$989.27	$989.30	$989.40