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	$249.80	3.737%	$259.135	$259.14	$259.15	$259.10
Purchase #2	$79.64	13.657%	$90.5164	$90.52	$90.50	$90.50
Purchase #3	$61.66	9.664%	$67.6188	$67.62	$67.60	$67.60
Purchase #4	$185.65	9.738%	$203.7286	$203.73	$203.75	$203.70
Purchase #5	$6.30	11.637%	$7.0331	$7.03	$7.05	$7.00
Purchase #6	$177.60	10.847%	$196.8643	$196.86	$196.85	$196.90
Purchase #7	$28.49	10.184%	$31.3914	$31.39	$31.40	$31.40
7 purchase totals =	$789.14		$856.2876	$856.29	$856.30	$856.20