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	$24.43	4.768%	$25.5948	$25.59	$25.60	$25.60
Purchase #2	$176.63	10.342%	$194.8971	$194.90	$194.90	$194.90
Purchase #3	$112.72	13.700%	$128.1626	$128.16	$128.15	$128.20
Purchase #4	$76.59	12.166%	$85.9079	$85.91	$85.90	$85.90
Purchase #5	$118.35	6.756%	$126.3457	$126.35	$126.35	$126.30
Purchase #6	$227.25	4.413%	$237.2785	$237.28	$237.30	$237.30
Purchase #7	$19.92	6.456%	$21.206	$21.21	$21.20	$21.20
7 purchase totals =	$755.89		$819.3926	$819.40	$819.40	$819.40