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	$228.47	9.210%	$249.5121	$249.51	$249.50	$249.50
Purchase #2	$67.55	5.143%	$71.0241	$71.02	$71.00	$71.00
Purchase #3	$104.30	12.571%	$117.4116	$117.41	$117.40	$117.40
Purchase #4	$14.64	7.168%	$15.6894	$15.69	$15.70	$15.70
Purchase #5	$103.62	13.350%	$117.4533	$117.45	$117.45	$117.50
Purchase #6	$35.58	13.659%	$40.4399	$40.44	$40.45	$40.40
Purchase #7	$41.30	3.388%	$42.6992	$42.70	$42.70	$42.70
7 purchase totals =	$595.46		$654.2296	$654.22	$654.20	$654.20