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	$187.29	10.443%	$206.8487	$206.85	$206.85	$206.80
Purchase #2	$67.70	7.271%	$72.6225	$72.62	$72.60	$72.60
Purchase #3	$26.82	5.104%	$28.1889	$28.19	$28.20	$28.20
Purchase #4	$172.69	13.728%	$196.3969	$196.40	$196.40	$196.40
Purchase #5	$42.84	12.549%	$48.216	$48.22	$48.20	$48.20
Purchase #6	$47.99	5.849%	$50.7969	$50.80	$50.80	$50.80
Purchase #7	$33.93	7.118%	$36.3451	$36.35	$36.35	$36.30
7 purchase totals =	$579.26		$639.4150	$639.43	$639.40	$639.30