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	$34.65	11.663%	$38.6912	$38.69	$38.70	$38.70
Purchase #2	$141.99	6.835%	$151.695	$151.70	$151.70	$151.70
Purchase #3	$113.77	4.416%	$118.7941	$118.79	$118.80	$118.80
Purchase #4	$220.92	5.795%	$233.7223	$233.72	$233.70	$233.70
Purchase #5	$90.79	9.649%	$99.5503	$99.55	$99.55	$99.60
Purchase #6	$145.85	11.567%	$162.7205	$162.72	$162.70	$162.70
Purchase #7	$230.41	12.544%	$259.3126	$259.31	$259.30	$259.30
7 purchase totals =	$978.38		$1,064.4860	$1,064.48	$1,064.45	$1,064.50