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	$42.31	8.167%	$45.7655	$45.77	$45.75	$45.80
Purchase #2	$172.67	12.156%	$193.6598	$193.66	$193.65	$193.70
Purchase #3	$67.87	8.257%	$73.474	$73.47	$73.45	$73.50
Purchase #4	$193.62	12.776%	$218.3569	$218.36	$218.35	$218.40
Purchase #5	$57.96	13.722%	$65.9133	$65.91	$65.90	$65.90
Purchase #6	$114.80	7.591%	$123.5145	$123.51	$123.50	$123.50
Purchase #7	$112.43	9.411%	$123.0108	$123.01	$123.00	$123.00
7 purchase totals =	$761.66		$843.6948	$843.69	$843.60	$843.80