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	$230.50	13.185%	$260.8914	$260.89	$260.90	$260.90
Purchase #2	$81.36	11.590%	$90.7896	$90.79	$90.80	$90.80
Purchase #3	$97.44	3.104%	$100.4645	$100.46	$100.45	$100.50
Purchase #4	$81.85	5.679%	$86.4983	$86.50	$86.50	$86.50
Purchase #5	$173.36	6.171%	$184.058	$184.06	$184.05	$184.10
Purchase #6	$51.46	10.657%	$56.9441	$56.94	$56.95	$56.90
Purchase #7	$183.87	7.610%	$197.8625	$197.86	$197.85	$197.90
7 purchase totals =	$899.84		$977.5084	$977.50	$977.50	$977.60