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	$90.74	9.200%	$99.0881	$99.09	$99.10	$99.10
Purchase #2	$126.73	12.723%	$142.8539	$142.85	$142.85	$142.90
Purchase #3	$169.25	7.216%	$181.4631	$181.46	$181.45	$181.50
Purchase #4	$137.76	4.404%	$143.827	$143.83	$143.85	$143.80
Purchase #5	$21.34	3.764%	$22.1432	$22.14	$22.15	$22.10
Purchase #6	$101.73	12.775%	$114.726	$114.73	$114.75	$114.70
Purchase #7	$118.88	5.541%	$125.4671	$125.47	$125.45	$125.50
7 purchase totals =	$766.43		$829.5684	$829.57	$829.60	$829.60