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	$137.60	13.737%	$156.5021	$156.50	$156.50	$156.50
Purchase #2	$54.32	6.726%	$57.9736	$57.97	$57.95	$58.00
Purchase #3	$168.99	6.500%	$179.9744	$179.97	$179.95	$180.00
Purchase #4	$230.51	10.577%	$254.891	$254.89	$254.90	$254.90
Purchase #5	$7.32	13.713%	$8.3238	$8.32	$8.30	$8.30
Purchase #6	$80.61	5.614%	$85.1354	$85.14	$85.15	$85.10
Purchase #7	$121.97	4.753%	$127.7672	$127.77	$127.75	$127.80
7 purchase totals =	$801.32		$870.5675	$870.56	$870.50	$870.60