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	$166.52	12.681%	$187.6364	$187.64	$187.65	$187.60
Purchase #2	$206.74	10.120%	$227.6621	$227.66	$227.65	$227.70
Purchase #3	$132.70	7.605%	$142.7918	$142.79	$142.80	$142.80
Purchase #4	$152.39	4.432%	$159.1439	$159.14	$159.15	$159.10
Purchase #5	$250.69	8.609%	$272.2719	$272.27	$272.25	$272.30
Purchase #6	$166.91	11.294%	$185.7608	$185.76	$185.75	$185.80
Purchase #7	$9.47	5.704%	$10.0102	$10.01	$10.00	$10.00
7 purchase totals =	$1,085.42		$1,185.2771	$1,185.27	$1,185.25	$1,185.30