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	$146.50	13.491%	$166.2643	$166.26	$166.25	$166.30
Purchase #2	$248.94	4.792%	$260.8692	$260.87	$260.85	$260.90
Purchase #3	$210.46	11.145%	$233.9158	$233.92	$233.90	$233.90
Purchase #4	$225.34	12.460%	$253.4174	$253.42	$253.40	$253.40
Purchase #5	$225.77	3.453%	$233.5658	$233.57	$233.55	$233.60
Purchase #6	$37.41	12.565%	$42.1106	$42.11	$42.10	$42.10
Purchase #7	$178.37	10.209%	$196.5798	$196.58	$196.60	$196.60
7 purchase totals =	$1,272.79		$1,386.7229	$1,386.73	$1,386.65	$1,386.80