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	$17.85	3.339%	$18.446	$18.45	$18.45	$18.40
Purchase #2	$249.45	3.754%	$258.8144	$258.81	$258.80	$258.80
Purchase #3	$59.55	13.301%	$67.4707	$67.47	$67.45	$67.50
Purchase #4	$148.85	13.671%	$169.1993	$169.20	$169.20	$169.20
Purchase #5	$186.76	7.309%	$200.4103	$200.41	$200.40	$200.40
Purchase #6	$45.59	11.857%	$50.9956	$51.00	$51.00	$51.00
Purchase #7	$133.57	8.390%	$144.7765	$144.78	$144.80	$144.80
7 purchase totals =	$841.62		$910.1128	$910.12	$910.10	$910.10