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	$43.99	4.153%	$45.8169	$45.82	$45.80	$45.80
Purchase #2	$196.38	6.825%	$209.7829	$209.78	$209.80	$209.80
Purchase #3	$94.42	4.285%	$98.4659	$98.47	$98.45	$98.50
Purchase #4	$76.96	5.500%	$81.1928	$81.19	$81.20	$81.20
Purchase #5	$11.28	10.616%	$12.4775	$12.48	$12.50	$12.50
Purchase #6	$33.90	11.720%	$37.8731	$37.87	$37.85	$37.90
Purchase #7	$12.45	13.543%	$14.1361	$14.14	$14.15	$14.10
7 purchase totals =	$469.38		$499.7452	$499.75	$499.75	$499.80