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	$18.52	12.492%	$20.8335	$20.83	$20.85	$20.80
Purchase #2	$139.76	7.326%	$149.9988	$150.00	$150.00	$150.00
Purchase #3	$110.38	9.641%	$121.0217	$121.02	$121.00	$121.00
Purchase #4	$161.55	6.605%	$172.2204	$172.22	$172.20	$172.20
Purchase #5	$99.34	7.242%	$106.5342	$106.53	$106.55	$106.50
Purchase #6	$132.87	6.788%	$141.8892	$141.89	$141.90	$141.90
Purchase #7	$11.38	6.473%	$12.1166	$12.12	$12.10	$12.10
7 purchase totals =	$673.80		$724.6144	$724.61	$724.60	$724.50