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	$87.62	12.536%	$98.604	$98.60	$98.60	$98.60
Purchase #2	$181.57	8.787%	$197.5246	$197.52	$197.50	$197.50
Purchase #3	$94.45	3.625%	$97.8738	$97.87	$97.85	$97.90
Purchase #4	$28.33	10.239%	$31.2307	$31.23	$31.25	$31.20
Purchase #5	$91.64	9.844%	$100.661	$100.66	$100.65	$100.70
Purchase #6	$64.70	11.370%	$72.0564	$72.06	$72.05	$72.10
Purchase #7	$47.75	10.273%	$52.6554	$52.66	$52.65	$52.70
7 purchase totals =	$596.06		$650.6059	$650.60	$650.55	$650.70