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	$143.68	3.619%	$148.8798	$148.88	$148.90	$148.90
Purchase #2	$188.30	12.397%	$211.6436	$211.64	$211.65	$211.60
Purchase #3	$29.72	9.371%	$32.5051	$32.51	$32.50	$32.50
Purchase #4	$139.27	11.463%	$155.2345	$155.23	$155.25	$155.20
Purchase #5	$98.86	12.468%	$111.1859	$111.19	$111.20	$111.20
Purchase #6	$167.59	11.285%	$186.5025	$186.50	$186.50	$186.50
Purchase #7	$65.34	4.712%	$68.4188	$68.42	$68.40	$68.40
7 purchase totals =	$832.76		$914.3702	$914.37	$914.40	$914.30