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	$42.40	6.227%	$45.0402	$45.04	$45.05	$45.00
Purchase #2	$27.78	6.159%	$29.491	$29.49	$29.50	$29.50
Purchase #3	$115.86	9.715%	$127.1158	$127.12	$127.10	$127.10
Purchase #4	$219.83	4.238%	$229.1464	$229.15	$229.15	$229.10
Purchase #5	$27.27	11.405%	$30.3801	$30.38	$30.40	$30.40
Purchase #6	$130.82	4.545%	$136.7658	$136.77	$136.75	$136.80
Purchase #7	$64.47	9.349%	$70.4973	$70.50	$70.50	$70.50
7 purchase totals =	$628.43		$668.4366	$668.45	$668.45	$668.40