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	$207.85	6.824%	$222.0337	$222.03	$222.05	$222.00
Purchase #2	$175.83	8.520%	$190.8107	$190.81	$190.80	$190.80
Purchase #3	$43.94	4.234%	$45.8004	$45.80	$45.80	$45.80
Purchase #4	$126.34	13.262%	$143.0952	$143.10	$143.10	$143.10
Purchase #5	$15.50	11.609%	$17.2994	$17.30	$17.30	$17.30
Purchase #6	$121.41	6.655%	$129.4898	$129.49	$129.50	$129.50
Purchase #7	$38.55	10.329%	$42.5318	$42.53	$42.55	$42.50
7 purchase totals =	$729.42		$791.0610	$791.06	$791.10	$791.00