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	$18.49	13.153%	$20.922	$20.92	$20.90	$20.90
Purchase #2	$19.81	4.249%	$20.6517	$20.65	$20.65	$20.70
Purchase #3	$152.99	12.340%	$171.869	$171.87	$171.85	$171.90
Purchase #4	$202.51	11.545%	$225.8898	$225.89	$225.90	$225.90
Purchase #5	$92.67	8.299%	$100.3607	$100.36	$100.35	$100.40
Purchase #6	$57.92	9.164%	$63.2278	$63.23	$63.25	$63.20
Purchase #7	$95.77	8.187%	$103.6107	$103.61	$103.60	$103.60
7 purchase totals =	$640.16		$706.5317	$706.53	$706.50	$706.60