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	$33.52	12.556%	$37.7288	$37.73	$37.75	$37.70
Purchase #2	$81.60	13.267%	$92.4259	$92.43	$92.45	$92.40
Purchase #3	$42.66	3.157%	$44.0068	$44.01	$44.00	$44.00
Purchase #4	$95.35	4.751%	$99.8801	$99.88	$99.90	$99.90
Purchase #5	$29.32	12.242%	$32.9094	$32.91	$32.90	$32.90
Purchase #6	$155.99	11.151%	$173.3844	$173.38	$173.40	$173.40
Purchase #7	$110.44	7.300%	$118.5021	$118.50	$118.50	$118.50
7 purchase totals =	$548.88		$598.8375	$598.84	$598.90	$598.80