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	$66.55	3.517%	$68.8906	$68.89	$68.90	$68.90
Purchase #2	$170.66	10.116%	$187.924	$187.92	$187.90	$187.90
Purchase #3	$82.82	13.801%	$94.25	$94.25	$94.25	$94.30
Purchase #4	$112.55	13.219%	$127.428	$127.43	$127.45	$127.40
Purchase #5	$173.83	4.776%	$182.1321	$182.13	$182.15	$182.10
Purchase #6	$65.75	10.642%	$72.7471	$72.75	$72.75	$72.70
Purchase #7	$91.91	5.480%	$96.9467	$96.95	$96.95	$96.90
7 purchase totals =	$764.07		$830.3185	$830.32	$830.35	$830.20