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	$24.58	13.604%	$27.9239	$27.92	$27.90	$27.90
Purchase #2	$14.72	3.505%	$15.2359	$15.24	$15.25	$15.20
Purchase #3	$208.91	11.702%	$233.3566	$233.36	$233.35	$233.40
Purchase #4	$73.89	11.332%	$82.2632	$82.26	$82.25	$82.30
Purchase #5	$233.97	11.723%	$261.3983	$261.40	$261.40	$261.40
Purchase #6	$172.87	4.673%	$180.9482	$180.95	$180.95	$180.90
Purchase #7	$210.56	3.125%	$217.14	$217.14	$217.15	$217.10
7 purchase totals =	$939.50		$1,018.2661	$1,018.27	$1,018.25	$1,018.20