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	$59.58	6.169%	$63.2555	$63.26	$63.25	$63.30
Purchase #2	$49.61	12.632%	$55.8767	$55.88	$55.90	$55.90
Purchase #3	$8.98	11.700%	$10.0307	$10.03	$10.05	$10.00
Purchase #4	$115.46	11.146%	$128.3292	$128.33	$128.35	$128.30
Purchase #5	$134.83	8.610%	$146.4389	$146.44	$146.45	$146.40
Purchase #6	$84.27	12.521%	$94.8214	$94.82	$94.80	$94.80
Purchase #7	$205.79	13.376%	$233.3165	$233.32	$233.30	$233.30
7 purchase totals =	$658.52		$732.0689	$732.08	$732.10	$732.00