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	$110.94	11.662%	$123.8778	$123.88	$123.90	$123.90
Purchase #2	$11.41	13.110%	$12.9059	$12.91	$12.90	$12.90
Purchase #3	$179.93	9.228%	$196.5339	$196.53	$196.55	$196.50
Purchase #4	$108.72	5.811%	$115.0377	$115.04	$115.05	$115.00
Purchase #5	$63.40	5.660%	$66.9884	$66.99	$67.00	$67.00
Purchase #6	$63.60	13.174%	$71.9787	$71.98	$72.00	$72.00
Purchase #7	$13.28	12.812%	$14.9814	$14.98	$15.00	$15.00
7 purchase totals =	$551.28		$602.3038	$602.31	$602.40	$602.30