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	$147.59	11.254%	$164.1998	$164.20	$164.20	$164.20
Purchase #2	$83.97	7.338%	$90.1317	$90.13	$90.15	$90.10
Purchase #3	$6.97	11.582%	$7.7773	$7.78	$7.80	$7.80
Purchase #4	$21.85	5.865%	$23.1315	$23.13	$23.15	$23.10
Purchase #5	$96.69	8.735%	$105.1359	$105.14	$105.15	$105.10
Purchase #6	$133.36	9.503%	$146.0332	$146.03	$146.05	$146.00
Purchase #7	$56.25	11.806%	$62.8909	$62.89	$62.90	$62.90
7 purchase totals =	$546.68		$599.3003	$599.30	$599.40	$599.20