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	$156.82	6.795%	$167.4759	$167.48	$167.50	$167.50
Purchase #2	$41.83	7.221%	$44.8505	$44.85	$44.85	$44.90
Purchase #3	$115.38	7.410%	$123.9297	$123.93	$123.95	$123.90
Purchase #4	$227.68	13.783%	$259.0611	$259.06	$259.05	$259.10
Purchase #5	$21.36	13.442%	$24.2312	$24.23	$24.25	$24.20
Purchase #6	$96.29	9.713%	$105.6426	$105.64	$105.65	$105.60
Purchase #7	$174.76	6.160%	$185.5252	$185.53	$185.55	$185.50
7 purchase totals =	$834.12		$910.7162	$910.72	$910.80	$910.70