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	$154.80	11.233%	$172.1887	$172.19	$172.20	$172.20
Purchase #2	$43.38	8.692%	$47.1506	$47.15	$47.15	$47.20
Purchase #3	$96.86	7.227%	$103.8601	$103.86	$103.85	$103.90
Purchase #4	$104.67	12.247%	$117.4889	$117.49	$117.50	$117.50
Purchase #5	$86.39	3.385%	$89.3143	$89.31	$89.30	$89.30
Purchase #6	$239.28	4.430%	$249.8801	$249.88	$249.90	$249.90
Purchase #7	$181.26	9.588%	$198.6392	$198.64	$198.65	$198.60
7 purchase totals =	$906.64		$978.5219	$978.52	$978.55	$978.60