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	$82.93	7.705%	$89.3198	$89.32	$89.30	$89.30
Purchase #2	$197.38	11.595%	$220.2662	$220.27	$220.25	$220.30
Purchase #3	$151.95	13.493%	$172.4526	$172.45	$172.45	$172.50
Purchase #4	$122.42	13.696%	$139.1866	$139.19	$139.20	$139.20
Purchase #5	$203.60	12.454%	$228.9563	$228.96	$228.95	$229.00
Purchase #6	$96.95	8.830%	$105.5107	$105.51	$105.50	$105.50
Purchase #7	$250.37	3.581%	$259.3357	$259.34	$259.35	$259.30
7 purchase totals =	$1,105.60		$1,215.0279	$1,215.04	$1,215.00	$1,215.10