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	$40.55	5.710%	$42.8654	$42.87	$42.85	$42.90
Purchase #2	$192.65	12.298%	$216.3421	$216.34	$216.35	$216.30
Purchase #3	$63.49	11.568%	$70.8345	$70.83	$70.85	$70.80
Purchase #4	$225.69	4.286%	$235.3631	$235.36	$235.35	$235.40
Purchase #5	$115.44	11.594%	$128.8241	$128.82	$128.80	$128.80
Purchase #6	$246.49	3.595%	$255.3513	$255.35	$255.35	$255.40
Purchase #7	$72.63	12.557%	$81.7501	$81.75	$81.75	$81.80
7 purchase totals =	$956.94		$1,031.3306	$1,031.32	$1,031.30	$1,031.40