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	$126.56	8.387%	$137.1746	$137.17	$137.15	$137.20
Purchase #2	$86.76	6.739%	$92.6068	$92.61	$92.60	$92.60
Purchase #3	$102.56	11.584%	$114.4406	$114.44	$114.45	$114.40
Purchase #4	$45.59	9.832%	$50.0724	$50.07	$50.05	$50.10
Purchase #5	$51.29	7.486%	$55.1296	$55.13	$55.15	$55.10
Purchase #6	$228.95	4.341%	$238.8887	$238.89	$238.90	$238.90
Purchase #7	$161.34	11.778%	$180.3426	$180.34	$180.35	$180.30
7 purchase totals =	$803.05		$868.6553	$868.65	$868.65	$868.60