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	$204.65	8.549%	$222.1455	$222.15	$222.15	$222.10
Purchase #2	$63.91	6.158%	$67.8456	$67.85	$67.85	$67.80
Purchase #3	$83.47	13.538%	$94.7702	$94.77	$94.75	$94.80
Purchase #4	$163.44	7.168%	$175.1554	$175.16	$175.15	$175.20
Purchase #5	$223.61	4.276%	$233.1716	$233.17	$233.15	$233.20
Purchase #6	$29.66	10.767%	$32.8535	$32.85	$32.85	$32.90
Purchase #7	$12.96	5.292%	$13.6458	$13.65	$13.65	$13.60
7 purchase totals =	$781.70		$839.5876	$839.60	$839.55	$839.60