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	$146.52	10.651%	$162.1258	$162.13	$162.15	$162.10
Purchase #2	$85.53	4.385%	$89.2805	$89.28	$89.30	$89.30
Purchase #3	$209.36	6.241%	$222.4262	$222.43	$222.45	$222.40
Purchase #4	$123.95	12.780%	$139.7908	$139.79	$139.80	$139.80
Purchase #5	$224.61	13.811%	$255.6309	$255.63	$255.65	$255.60
Purchase #6	$133.82	8.444%	$145.1198	$145.12	$145.10	$145.10
Purchase #7	$131.47	3.601%	$136.2042	$136.20	$136.20	$136.20
7 purchase totals =	$1,055.26		$1,150.5782	$1,150.58	$1,150.65	$1,150.50