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	$99.33	8.705%	$107.9767	$107.98	$108.00	$108.00
Purchase #2	$236.57	10.250%	$260.8184	$260.82	$260.80	$260.80
Purchase #3	$204.31	13.360%	$231.6058	$231.61	$231.60	$231.60
Purchase #4	$193.33	3.165%	$199.4489	$199.45	$199.45	$199.40
Purchase #5	$142.45	6.601%	$151.8531	$151.85	$151.85	$151.90
Purchase #6	$34.86	12.692%	$39.2844	$39.28	$39.30	$39.30
Purchase #7	$91.27	4.435%	$95.3178	$95.32	$95.30	$95.30
7 purchase totals =	$1,002.12		$1,086.3051	$1,086.31	$1,086.30	$1,086.30