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	$109.86	12.773%	$123.8924	$123.89	$123.90	$123.90
Purchase #2	$15.58	3.715%	$16.1588	$16.16	$16.15	$16.20
Purchase #3	$236.30	8.393%	$256.1327	$256.13	$256.15	$256.10
Purchase #4	$91.92	10.538%	$101.6065	$101.61	$101.60	$101.60
Purchase #5	$81.76	8.612%	$88.8012	$88.80	$88.80	$88.80
Purchase #6	$39.98	11.384%	$44.5313	$44.53	$44.55	$44.50
Purchase #7	$40.72	11.595%	$45.4415	$45.44	$45.45	$45.40
7 purchase totals =	$616.12		$676.5644	$676.56	$676.60	$676.50