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	$127.81	12.545%	$143.8438	$143.84	$143.85	$143.80
Purchase #2	$139.41	6.329%	$148.2333	$148.23	$148.25	$148.20
Purchase #3	$83.84	7.158%	$89.8413	$89.84	$89.85	$89.80
Purchase #4	$137.45	8.789%	$149.5305	$149.53	$149.55	$149.50
Purchase #5	$88.45	10.206%	$97.4772	$97.48	$97.50	$97.50
Purchase #6	$47.53	13.192%	$53.8002	$53.80	$53.80	$53.80
Purchase #7	$173.85	7.468%	$186.8331	$186.83	$186.85	$186.80
7 purchase totals =	$798.34		$869.5594	$869.55	$869.65	$869.40