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	$12.65	9.563%	$13.8597	$13.86	$13.85	$13.90
Purchase #2	$155.31	9.782%	$170.5024	$170.50	$170.50	$170.50
Purchase #3	$112.72	4.269%	$117.532	$117.53	$117.55	$117.50
Purchase #4	$91.59	9.680%	$100.4559	$100.46	$100.45	$100.50
Purchase #5	$13.69	12.329%	$15.3778	$15.38	$15.40	$15.40
Purchase #6	$14.75	4.828%	$15.4621	$15.46	$15.45	$15.50
Purchase #7	$36.61	10.735%	$40.5401	$40.54	$40.55	$40.50
7 purchase totals =	$437.32		$473.7300	$473.73	$473.75	$473.80