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	$75.59	10.219%	$83.3145	$83.31	$83.30	$83.30
Purchase #2	$206.61	9.801%	$226.8598	$226.86	$226.85	$226.90
Purchase #3	$49.71	7.520%	$53.4482	$53.45	$53.45	$53.40
Purchase #4	$145.55	9.310%	$159.1007	$159.10	$159.10	$159.10
Purchase #5	$119.62	3.615%	$123.9443	$123.94	$123.95	$123.90
Purchase #6	$58.54	13.704%	$66.5623	$66.56	$66.55	$66.60
Purchase #7	$89.52	7.513%	$96.2456	$96.25	$96.25	$96.20
7 purchase totals =	$745.14		$809.4754	$809.47	$809.45	$809.40