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	$119.45	3.759%	$123.9401	$123.94	$123.95	$123.90
Purchase #2	$97.81	11.559%	$109.1159	$109.12	$109.10	$109.10
Purchase #3	$48.37	13.600%	$54.9483	$54.95	$54.95	$54.90
Purchase #4	$29.60	5.454%	$31.2144	$31.21	$31.20	$31.20
Purchase #5	$241.73	10.741%	$267.6942	$267.69	$267.70	$267.70
Purchase #6	$133.30	13.417%	$151.1849	$151.18	$151.20	$151.20
Purchase #7	$141.34	8.487%	$153.3355	$153.34	$153.35	$153.30
7 purchase totals =	$811.60		$891.4333	$891.43	$891.45	$891.30