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	$29.65	4.741%	$31.0557	$31.06	$31.05	$31.10
Purchase #2	$27.60	8.110%	$29.8384	$29.84	$29.85	$29.80
Purchase #3	$162.62	4.306%	$169.6224	$169.62	$169.60	$169.60
Purchase #4	$100.65	4.788%	$105.4691	$105.47	$105.45	$105.50
Purchase #5	$75.30	9.873%	$82.7344	$82.73	$82.75	$82.70
Purchase #6	$183.40	7.390%	$196.9533	$196.95	$196.95	$197.00
Purchase #7	$153.94	5.543%	$162.4729	$162.47	$162.45	$162.50
7 purchase totals =	$733.16		$778.1462	$778.14	$778.10	$778.20