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	$19.45	4.604%	$20.3455	$20.35	$20.35	$20.30
Purchase #2	$206.60	5.663%	$218.2998	$218.30	$218.30	$218.30
Purchase #3	$172.60	4.635%	$180.6	$180.60	$180.60	$180.60
Purchase #4	$99.57	9.405%	$108.9346	$108.93	$108.95	$108.90
Purchase #5	$153.57	12.403%	$172.6173	$172.62	$172.60	$172.60
Purchase #6	$148.64	13.440%	$168.6172	$168.62	$168.60	$168.60
Purchase #7	$51.30	10.417%	$56.6439	$56.64	$56.65	$56.60
7 purchase totals =	$851.73		$926.0583	$926.06	$926.05	$925.90