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	$26.93	8.379%	$29.1865	$29.19	$29.20	$29.20
Purchase #2	$45.39	6.830%	$48.4901	$48.49	$48.50	$48.50
Purchase #3	$135.25	4.314%	$141.0847	$141.08	$141.10	$141.10
Purchase #4	$26.28	8.854%	$28.6068	$28.61	$28.60	$28.60
Purchase #5	$188.77	5.811%	$199.7394	$199.74	$199.75	$199.70
Purchase #6	$38.46	4.405%	$40.1542	$40.15	$40.15	$40.20
Purchase #7	$172.96	7.322%	$185.6241	$185.62	$185.60	$185.60
7 purchase totals =	$634.04		$672.8858	$672.88	$672.90	$672.90