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	$45.31	6.213%	$48.1251	$48.13	$48.15	$48.10
Purchase #2	$143.43	3.810%	$148.8947	$148.89	$148.90	$148.90
Purchase #3	$111.85	6.231%	$118.8194	$118.82	$118.80	$118.80
Purchase #4	$227.34	5.857%	$240.6553	$240.66	$240.65	$240.70
Purchase #5	$87.54	5.675%	$92.5079	$92.51	$92.50	$92.50
Purchase #6	$250.68	5.540%	$264.5677	$264.57	$264.55	$264.60
Purchase #7	$162.74	8.517%	$176.6006	$176.60	$176.60	$176.60
7 purchase totals =	$1,028.89		$1,090.1707	$1,090.18	$1,090.15	$1,090.20