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	$133.40	13.603%	$151.5464	$151.55	$151.55	$151.50
Purchase #2	$103.75	5.329%	$109.2788	$109.28	$109.30	$109.30
Purchase #3	$28.64	13.591%	$32.5325	$32.53	$32.55	$32.50
Purchase #4	$169.52	10.616%	$187.5162	$187.52	$187.50	$187.50
Purchase #5	$113.55	13.688%	$129.0927	$129.09	$129.10	$129.10
Purchase #6	$38.66	4.130%	$40.2567	$40.26	$40.25	$40.30
Purchase #7	$216.93	10.301%	$239.276	$239.28	$239.30	$239.30
7 purchase totals =	$804.45		$889.4993	$889.51	$889.55	$889.50