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	$77.52	6.396%	$82.4782	$82.48	$82.50	$82.50
Purchase #2	$93.33	13.481%	$105.9118	$105.91	$105.90	$105.90
Purchase #3	$192.33	10.779%	$213.0613	$213.06	$213.05	$213.10
Purchase #4	$119.31	3.603%	$123.6087	$123.61	$123.60	$123.60
Purchase #5	$95.65	8.773%	$104.0414	$104.04	$104.05	$104.00
Purchase #6	$24.76	6.141%	$26.2805	$26.28	$26.30	$26.30
Purchase #7	$9.33	4.861%	$9.7835	$9.78	$9.80	$9.80
7 purchase totals =	$612.23		$665.1654	$665.16	$665.20	$665.20