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	$78.53	6.180%	$83.3832	$83.38	$83.40	$83.40
Purchase #2	$115.30	12.829%	$130.0918	$130.09	$130.10	$130.10
Purchase #3	$167.48	3.218%	$172.8695	$172.87	$172.85	$172.90
Purchase #4	$119.75	12.282%	$134.4577	$134.46	$134.45	$134.50
Purchase #5	$75.89	8.783%	$82.5554	$82.56	$82.55	$82.60
Purchase #6	$9.56	7.192%	$10.2476	$10.25	$10.25	$10.20
Purchase #7	$195.63	6.827%	$208.9857	$208.99	$209.00	$209.00
7 purchase totals =	$762.14		$822.5909	$822.60	$822.60	$822.70