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	$16.41	13.478%	$18.6217	$18.62	$18.60	$18.60
Purchase #2	$89.34	12.381%	$100.4012	$100.40	$100.40	$100.40
Purchase #3	$227.59	3.586%	$235.7514	$235.75	$235.75	$235.80
Purchase #4	$211.58	10.397%	$233.578	$233.58	$233.60	$233.60
Purchase #5	$225.52	5.443%	$237.7951	$237.80	$237.80	$237.80
Purchase #6	$10.60	10.516%	$11.7147	$11.71	$11.70	$11.70
Purchase #7	$223.71	8.744%	$243.2712	$243.27	$243.25	$243.30
7 purchase totals =	$1,004.75		$1,081.1333	$1,081.13	$1,081.10	$1,081.20