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	$87.31	3.220%	$90.1214	$90.12	$90.10	$90.10
Purchase #2	$149.98	6.157%	$159.2143	$159.21	$159.20	$159.20
Purchase #3	$73.41	6.580%	$78.2404	$78.24	$78.25	$78.20
Purchase #4	$213.41	9.753%	$234.2239	$234.22	$234.20	$234.20
Purchase #5	$224.27	13.714%	$255.0264	$255.03	$255.05	$255.00
Purchase #6	$21.79	12.634%	$24.5429	$24.54	$24.55	$24.50
Purchase #7	$52.60	11.193%	$58.4875	$58.49	$58.50	$58.50
7 purchase totals =	$822.77		$899.8568	$899.85	$899.85	$899.70