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	$180.47	3.380%	$186.5699	$186.57	$186.55	$186.60
Purchase #2	$50.42	7.605%	$54.2544	$54.25	$54.25	$54.30
Purchase #3	$68.41	13.544%	$77.6755	$77.68	$77.70	$77.70
Purchase #4	$50.88	7.656%	$54.7754	$54.78	$54.80	$54.80
Purchase #5	$229.51	5.278%	$241.6235	$241.62	$241.60	$241.60
Purchase #6	$190.80	11.327%	$212.4119	$212.41	$212.40	$212.40
Purchase #7	$69.34	4.188%	$72.244	$72.24	$72.25	$72.20
7 purchase totals =	$839.83		$899.5546	$899.55	$899.55	$899.60