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	$37.31	4.156%	$38.8606	$38.86	$38.85	$38.90
Purchase #2	$202.69	13.435%	$229.9214	$229.92	$229.90	$229.90
Purchase #3	$91.94	5.440%	$96.9415	$96.94	$96.95	$96.90
Purchase #4	$31.91	3.553%	$33.0438	$33.04	$33.05	$33.00
Purchase #5	$177.65	6.151%	$188.5773	$188.58	$188.60	$188.60
Purchase #6	$125.98	11.487%	$140.4513	$140.45	$140.45	$140.50
Purchase #7	$66.89	9.114%	$72.9864	$72.99	$73.00	$73.00
7 purchase totals =	$734.37		$800.7823	$800.78	$800.80	$800.80