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	$21.89	13.531%	$24.8519	$24.85	$24.85	$24.90
Purchase #2	$111.42	10.642%	$123.2773	$123.28	$123.30	$123.30
Purchase #3	$90.66	10.264%	$99.9653	$99.97	$99.95	$100.00
Purchase #4	$114.62	4.711%	$120.0197	$120.02	$120.00	$120.00
Purchase #5	$176.77	6.344%	$187.9843	$187.98	$188.00	$188.00
Purchase #6	$41.76	3.600%	$43.2634	$43.26	$43.25	$43.30
Purchase #7	$212.89	13.745%	$242.1517	$242.15	$242.15	$242.20
7 purchase totals =	$770.01		$841.5136	$841.51	$841.50	$841.70