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	$130.32	6.840%	$139.2339	$139.23	$139.25	$139.20
Purchase #2	$227.35	7.116%	$243.5282	$243.53	$243.55	$243.50
Purchase #3	$40.28	5.575%	$42.5256	$42.53	$42.55	$42.50
Purchase #4	$144.97	10.464%	$160.1397	$160.14	$160.15	$160.10
Purchase #5	$52.44	6.477%	$55.8365	$55.84	$55.85	$55.80
Purchase #6	$214.69	3.847%	$222.9491	$222.95	$222.95	$222.90
Purchase #7	$79.77	4.410%	$83.2879	$83.29	$83.30	$83.30
7 purchase totals =	$889.82		$947.5009	$947.51	$947.60	$947.30