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	$206.63	7.535%	$222.1996	$222.20	$222.20	$222.20
Purchase #2	$111.50	6.362%	$118.5936	$118.59	$118.60	$118.60
Purchase #3	$90.92	13.713%	$103.3879	$103.39	$103.40	$103.40
Purchase #4	$155.57	8.202%	$168.3299	$168.33	$168.35	$168.30
Purchase #5	$46.85	10.497%	$51.7678	$51.77	$51.75	$51.80
Purchase #6	$40.55	5.288%	$42.6943	$42.69	$42.70	$42.70
Purchase #7	$53.60	9.443%	$58.6614	$58.66	$58.65	$58.70
7 purchase totals =	$705.62		$765.6345	$765.63	$765.65	$765.70