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	$91.94	8.413%	$99.6749	$99.67	$99.65	$99.70
Purchase #2	$72.74	12.193%	$81.6092	$81.61	$81.60	$81.60
Purchase #3	$207.84	5.316%	$218.8888	$218.89	$218.90	$218.90
Purchase #4	$120.75	8.394%	$130.8858	$130.89	$130.90	$130.90
Purchase #5	$207.44	10.618%	$229.466	$229.47	$229.45	$229.50
Purchase #6	$129.46	13.491%	$146.9254	$146.93	$146.95	$146.90
Purchase #7	$155.67	11.139%	$173.0101	$173.01	$173.00	$173.00
7 purchase totals =	$985.84		$1,080.4602	$1,080.47	$1,080.45	$1,080.50