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	$101.92	4.596%	$106.6042	$106.60	$106.60	$106.60
Purchase #2	$153.88	9.711%	$168.8233	$168.82	$168.80	$168.80
Purchase #3	$242.42	4.725%	$253.8743	$253.87	$253.85	$253.90
Purchase #4	$241.86	10.400%	$267.0134	$267.01	$267.00	$267.00
Purchase #5	$36.29	7.217%	$38.909	$38.91	$38.90	$38.90
Purchase #6	$160.70	7.821%	$173.2683	$173.27	$173.25	$173.30
Purchase #7	$77.69	13.125%	$87.8868	$87.89	$87.90	$87.90
7 purchase totals =	$1,014.76		$1,096.3793	$1,096.37	$1,096.30	$1,096.40