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	$222.83	7.176%	$238.8203	$238.82	$238.80	$238.80
Purchase #2	$109.26	13.229%	$123.714	$123.71	$123.70	$123.70
Purchase #3	$28.56	3.682%	$29.6116	$29.61	$29.60	$29.60
Purchase #4	$78.82	10.175%	$86.8399	$86.84	$86.85	$86.80
Purchase #5	$33.90	6.337%	$36.0482	$36.05	$36.05	$36.00
Purchase #6	$220.27	10.425%	$243.2331	$243.23	$243.25	$243.20
Purchase #7	$81.55	4.701%	$85.3837	$85.38	$85.40	$85.40
7 purchase totals =	$775.19		$843.6508	$843.64	$843.65	$843.50