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	$107.50	11.755%	$120.1366	$120.14	$120.15	$120.10
Purchase #2	$188.86	3.568%	$195.5985	$195.60	$195.60	$195.60
Purchase #3	$250.75	13.798%	$285.3485	$285.35	$285.35	$285.30
Purchase #4	$87.91	3.409%	$90.9069	$90.91	$90.90	$90.90
Purchase #5	$193.89	12.280%	$217.6997	$217.70	$217.70	$217.70
Purchase #6	$72.89	13.641%	$82.8329	$82.83	$82.85	$82.80
Purchase #7	$82.99	8.170%	$89.7703	$89.77	$89.75	$89.80
7 purchase totals =	$984.79		$1,082.2934	$1,082.30	$1,082.30	$1,082.20