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	$119.77	9.693%	$131.3793	$131.38	$131.40	$131.40
Purchase #2	$61.35	7.867%	$66.1764	$66.18	$66.20	$66.20
Purchase #3	$19.66	7.628%	$21.1597	$21.16	$21.15	$21.20
Purchase #4	$133.42	10.674%	$147.6613	$147.66	$147.65	$147.70
Purchase #5	$78.38	13.716%	$89.1306	$89.13	$89.15	$89.10
Purchase #6	$217.44	5.153%	$228.6447	$228.64	$228.65	$228.60
Purchase #7	$149.46	11.454%	$166.5791	$166.58	$166.60	$166.60
7 purchase totals =	$779.48		$850.7311	$850.73	$850.80	$850.80