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	$166.85	12.328%	$187.4193	$187.42	$187.40	$187.40
Purchase #2	$87.32	3.358%	$90.2522	$90.25	$90.25	$90.30
Purchase #3	$40.39	5.541%	$42.628	$42.63	$42.65	$42.60
Purchase #4	$18.44	4.802%	$19.3255	$19.33	$19.35	$19.30
Purchase #5	$216.96	4.754%	$227.2743	$227.27	$227.25	$227.30
Purchase #6	$91.92	9.414%	$100.5733	$100.57	$100.55	$100.60
Purchase #7	$16.42	3.129%	$16.9338	$16.93	$16.95	$16.90
7 purchase totals =	$638.30		$684.4064	$684.40	$684.40	$684.40