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	$202.78	6.478%	$215.9161	$215.92	$215.90	$215.90
Purchase #2	$81.97	10.273%	$90.3908	$90.39	$90.40	$90.40
Purchase #3	$60.98	4.418%	$63.6741	$63.67	$63.65	$63.70
Purchase #4	$93.68	7.615%	$100.8137	$100.81	$100.80	$100.80
Purchase #5	$72.93	9.499%	$79.8576	$79.86	$79.85	$79.90
Purchase #6	$188.39	8.553%	$204.503	$204.50	$204.50	$204.50
Purchase #7	$80.74	10.416%	$89.1499	$89.15	$89.15	$89.10
7 purchase totals =	$781.47		$844.3052	$844.30	$844.25	$844.30