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	$134.32	7.819%	$144.8225	$144.82	$144.80	$144.80
Purchase #2	$200.92	13.758%	$228.5626	$228.56	$228.55	$228.60
Purchase #3	$19.82	4.873%	$20.7858	$20.79	$20.80	$20.80
Purchase #4	$35.35	12.797%	$39.8737	$39.87	$39.85	$39.90
Purchase #5	$40.29	3.214%	$41.5849	$41.58	$41.60	$41.60
Purchase #6	$134.74	5.497%	$142.1467	$142.15	$142.15	$142.10
Purchase #7	$45.63	7.110%	$48.8743	$48.87	$48.85	$48.90
7 purchase totals =	$611.07		$666.6505	$666.64	$666.60	$666.70