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	$96.60	8.156%	$104.4787	$104.48	$104.50	$104.50
Purchase #2	$122.61	13.332%	$138.9564	$138.96	$138.95	$139.00
Purchase #3	$83.85	13.820%	$95.4381	$95.44	$95.45	$95.40
Purchase #4	$76.30	4.280%	$79.5656	$79.57	$79.55	$79.60
Purchase #5	$37.70	7.411%	$40.4939	$40.49	$40.50	$40.50
Purchase #6	$150.60	9.704%	$165.2142	$165.21	$165.20	$165.20
Purchase #7	$89.57	11.137%	$99.5454	$99.55	$99.55	$99.50
7 purchase totals =	$657.23		$723.6923	$723.70	$723.70	$723.70