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	$59.90	10.610%	$66.2554	$66.26	$66.25	$66.30
Purchase #2	$146.61	6.621%	$156.317	$156.32	$156.30	$156.30
Purchase #3	$210.67	4.578%	$220.3145	$220.31	$220.30	$220.30
Purchase #4	$41.66	6.700%	$44.4512	$44.45	$44.45	$44.50
Purchase #5	$101.36	9.796%	$111.2892	$111.29	$111.30	$111.30
Purchase #6	$247.75	5.442%	$261.2326	$261.23	$261.25	$261.20
Purchase #7	$193.87	8.505%	$210.3586	$210.36	$210.35	$210.40
7 purchase totals =	$1,001.82		$1,070.2185	$1,070.22	$1,070.20	$1,070.30