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	$131.59	6.331%	$139.921	$139.92	$139.90	$139.90
Purchase #2	$186.39	9.262%	$203.6534	$203.65	$203.65	$203.70
Purchase #3	$15.39	9.805%	$16.899	$16.90	$16.90	$16.90
Purchase #4	$105.76	5.560%	$111.6403	$111.64	$111.65	$111.60
Purchase #5	$96.55	4.264%	$100.6669	$100.67	$100.65	$100.70
Purchase #6	$48.57	3.528%	$50.2835	$50.28	$50.30	$50.30
Purchase #7	$219.61	6.301%	$233.4476	$233.45	$233.45	$233.40
7 purchase totals =	$803.86		$856.5117	$856.51	$856.50	$856.50