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	$21.44	6.683%	$22.8728	$22.87	$22.85	$22.90
Purchase #2	$39.79	10.749%	$44.067	$44.07	$44.05	$44.10
Purchase #3	$79.51	13.605%	$90.3273	$90.33	$90.35	$90.30
Purchase #4	$104.79	10.269%	$115.5509	$115.55	$115.55	$115.60
Purchase #5	$32.94	13.157%	$37.2739	$37.27	$37.25	$37.30
Purchase #6	$169.44	8.301%	$183.5052	$183.51	$183.50	$183.50
Purchase #7	$39.65	5.799%	$41.9493	$41.95	$41.95	$41.90
7 purchase totals =	$487.56		$535.5464	$535.55	$535.50	$535.60