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	$38.45	11.617%	$42.9167	$42.92	$42.90	$42.90
Purchase #2	$84.97	5.224%	$89.4088	$89.41	$89.40	$89.40
Purchase #3	$79.59	13.195%	$90.0919	$90.09	$90.10	$90.10
Purchase #4	$10.86	11.800%	$12.1415	$12.14	$12.15	$12.10
Purchase #5	$89.82	3.759%	$93.1963	$93.20	$93.20	$93.20
Purchase #6	$67.91	8.169%	$73.4576	$73.46	$73.45	$73.50
Purchase #7	$17.82	11.866%	$19.9345	$19.93	$19.95	$19.90
7 purchase totals =	$389.42		$421.1473	$421.15	$421.15	$421.10