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	$39.58	7.492%	$42.5453	$42.55	$42.55	$42.50
Purchase #2	$152.60	13.262%	$172.8378	$172.84	$172.85	$172.80
Purchase #3	$51.87	4.808%	$54.3639	$54.36	$54.35	$54.40
Purchase #4	$46.83	11.807%	$52.3592	$52.36	$52.35	$52.40
Purchase #5	$223.48	8.855%	$243.2692	$243.27	$243.25	$243.30
Purchase #6	$15.93	13.239%	$18.039	$18.04	$18.05	$18.00
Purchase #7	$44.57	11.698%	$49.7838	$49.78	$49.80	$49.80
7 purchase totals =	$574.86		$633.1982	$633.20	$633.20	$633.20