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	$130.55	6.491%	$139.024	$139.02	$139.00	$139.00
Purchase #2	$246.76	10.314%	$272.2108	$272.21	$272.20	$272.20
Purchase #3	$245.58	3.491%	$254.1532	$254.15	$254.15	$254.20
Purchase #4	$49.29	3.789%	$51.1576	$51.16	$51.15	$51.20
Purchase #5	$210.54	5.683%	$222.505	$222.51	$222.50	$222.50
Purchase #6	$135.59	13.822%	$154.3312	$154.33	$154.35	$154.30
Purchase #7	$77.28	6.468%	$82.2785	$82.28	$82.30	$82.30
7 purchase totals =	$1,095.59		$1,175.6603	$1,175.66	$1,175.65	$1,175.70