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	$102.37	7.302%	$109.8451	$109.85	$109.85	$109.80
Purchase #2	$166.43	13.568%	$189.0112	$189.01	$189.00	$189.00
Purchase #3	$184.31	10.290%	$203.2755	$203.28	$203.30	$203.30
Purchase #4	$147.41	4.184%	$153.5776	$153.58	$153.60	$153.60
Purchase #5	$99.51	12.704%	$112.1518	$112.15	$112.15	$112.20
Purchase #6	$12.82	11.706%	$14.3207	$14.32	$14.30	$14.30
Purchase #7	$171.58	5.121%	$180.3666	$180.37	$180.35	$180.40
7 purchase totals =	$884.43		$962.5485	$962.56	$962.55	$962.60