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	$83.30	10.116%	$91.7266	$91.73	$91.75	$91.70
Purchase #2	$176.32	8.277%	$190.914	$190.91	$190.90	$190.90
Purchase #3	$168.68	5.149%	$177.3653	$177.37	$177.35	$177.40
Purchase #4	$41.77	9.289%	$45.65	$45.65	$45.65	$45.70
Purchase #5	$116.61	12.200%	$130.8364	$130.84	$130.85	$130.80
Purchase #6	$128.85	8.342%	$139.5987	$139.60	$139.60	$139.60
Purchase #7	$157.78	5.318%	$166.1707	$166.17	$166.15	$166.20
7 purchase totals =	$873.31		$942.2617	$942.27	$942.25	$942.30