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	$80.40	12.579%	$90.5135	$90.51	$90.50	$90.50
Purchase #2	$35.34	4.801%	$37.0367	$37.04	$37.05	$37.00
Purchase #3	$115.94	10.317%	$127.9015	$127.90	$127.90	$127.90
Purchase #4	$93.78	7.521%	$100.8332	$100.83	$100.85	$100.80
Purchase #5	$188.85	9.380%	$206.5641	$206.56	$206.55	$206.60
Purchase #6	$19.57	5.287%	$20.6047	$20.60	$20.60	$20.60
Purchase #7	$58.25	3.652%	$60.3773	$60.38	$60.40	$60.40
7 purchase totals =	$592.13		$643.8310	$643.82	$643.85	$643.80