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	$24.87	10.619%	$27.5109	$27.51	$27.50	$27.50
Purchase #2	$99.71	13.248%	$112.9196	$112.92	$112.90	$112.90
Purchase #3	$68.39	6.549%	$72.8689	$72.87	$72.85	$72.90
Purchase #4	$9.87	9.407%	$10.7985	$10.80	$10.80	$10.80
Purchase #5	$151.71	3.373%	$156.8272	$156.83	$156.85	$156.80
Purchase #6	$82.79	7.701%	$89.1657	$89.17	$89.15	$89.20
Purchase #7	$138.48	10.467%	$152.9747	$152.97	$152.95	$153.00
7 purchase totals =	$575.82		$623.0655	$623.07	$623.00	$623.10