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	$60.57	12.565%	$68.1806	$68.18	$68.20	$68.20
Purchase #2	$181.82	7.460%	$195.3838	$195.38	$195.40	$195.40
Purchase #3	$16.89	9.792%	$18.5439	$18.54	$18.55	$18.50
Purchase #4	$88.42	13.825%	$100.6441	$100.64	$100.65	$100.60
Purchase #5	$238.84	10.713%	$264.4269	$264.43	$264.45	$264.40
Purchase #6	$187.50	12.308%	$210.5775	$210.58	$210.60	$210.60
Purchase #7	$91.96	7.743%	$99.0805	$99.08	$99.10	$99.10
7 purchase totals =	$866.00		$956.8373	$956.83	$956.95	$956.80