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	$67.53	4.313%	$70.4426	$70.44	$70.45	$70.40
Purchase #2	$141.45	9.245%	$154.5271	$154.53	$154.55	$154.50
Purchase #3	$116.34	13.825%	$132.424	$132.42	$132.40	$132.40
Purchase #4	$11.35	8.501%	$12.3149	$12.31	$12.30	$12.30
Purchase #5	$42.68	6.543%	$45.4726	$45.47	$45.45	$45.50
Purchase #6	$72.49	8.454%	$78.6183	$78.62	$78.60	$78.60
Purchase #7	$18.60	8.428%	$20.1676	$20.17	$20.15	$20.20
7 purchase totals =	$470.44		$513.9671	$513.96	$513.90	$513.90