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	$90.91	9.139%	$99.2183	$99.22	$99.20	$99.20
Purchase #2	$171.38	10.612%	$189.5668	$189.57	$189.55	$189.60
Purchase #3	$167.50	4.485%	$175.0124	$175.01	$175.00	$175.00
Purchase #4	$59.62	6.388%	$63.4285	$63.43	$63.45	$63.40
Purchase #5	$31.77	5.757%	$33.599	$33.60	$33.60	$33.60
Purchase #6	$154.47	5.799%	$163.4277	$163.43	$163.45	$163.40
Purchase #7	$68.25	5.402%	$71.9369	$71.94	$71.95	$71.90
7 purchase totals =	$743.90		$796.1896	$796.20	$796.20	$796.10