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	$136.88	4.708%	$143.3243	$143.32	$143.30	$143.30
Purchase #2	$71.42	10.713%	$79.0712	$79.07	$79.05	$79.10
Purchase #3	$135.44	12.352%	$152.1695	$152.17	$152.15	$152.20
Purchase #4	$176.80	6.776%	$188.78	$188.78	$188.80	$188.80
Purchase #5	$169.48	8.587%	$184.0332	$184.03	$184.05	$184.00
Purchase #6	$136.69	5.725%	$144.5155	$144.52	$144.50	$144.50
Purchase #7	$97.77	8.286%	$105.8712	$105.87	$105.85	$105.90
7 purchase totals =	$924.48		$997.7649	$997.76	$997.70	$997.80