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	$129.41	13.813%	$147.2854	$147.29	$147.30	$147.30
Purchase #2	$144.39	6.253%	$153.4187	$153.42	$153.40	$153.40
Purchase #3	$109.67	8.127%	$118.5829	$118.58	$118.60	$118.60
Purchase #4	$179.41	9.518%	$196.4862	$196.49	$196.50	$196.50
Purchase #5	$169.93	9.277%	$185.6944	$185.69	$185.70	$185.70
Purchase #6	$78.99	3.125%	$81.4584	$81.46	$81.45	$81.50
Purchase #7	$30.93	9.477%	$33.8612	$33.86	$33.85	$33.90
7 purchase totals =	$842.73		$916.7872	$916.79	$916.80	$916.90