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	$77.60	9.818%	$85.2188	$85.22	$85.20	$85.20
Purchase #2	$107.55	11.256%	$119.6558	$119.66	$119.65	$119.70
Purchase #3	$214.32	11.330%	$238.6025	$238.60	$238.60	$238.60
Purchase #4	$164.75	4.260%	$171.7684	$171.77	$171.75	$171.80
Purchase #5	$98.87	4.409%	$103.2292	$103.23	$103.25	$103.20
Purchase #6	$65.87	5.428%	$69.4454	$69.45	$69.45	$69.40
Purchase #7	$191.35	7.583%	$205.8601	$205.86	$205.85	$205.90
7 purchase totals =	$920.31		$993.7802	$993.79	$993.75	$993.80