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	$76.99	4.481%	$80.4399	$80.44	$80.45	$80.40
Purchase #2	$83.86	13.726%	$95.3706	$95.37	$95.35	$95.40
Purchase #3	$171.30	5.152%	$180.1254	$180.13	$180.15	$180.10
Purchase #4	$58.82	13.131%	$66.5437	$66.54	$66.55	$66.50
Purchase #5	$41.60	4.457%	$43.4541	$43.45	$43.45	$43.50
Purchase #6	$5.90	4.190%	$6.1472	$6.15	$6.15	$6.10
Purchase #7	$14.61	4.619%	$15.2848	$15.28	$15.30	$15.30
7 purchase totals =	$453.08		$487.3657	$487.36	$487.40	$487.30