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	$132.68	11.784%	$148.315	$148.32	$148.30	$148.30
Purchase #2	$48.39	5.796%	$51.1947	$51.19	$51.20	$51.20
Purchase #3	$38.39	6.540%	$40.9007	$40.90	$40.90	$40.90
Purchase #4	$151.57	9.292%	$165.6539	$165.65	$165.65	$165.70
Purchase #5	$63.68	5.454%	$67.1531	$67.15	$67.15	$67.20
Purchase #6	$13.43	4.696%	$14.0607	$14.06	$14.05	$14.10
Purchase #7	$158.61	12.303%	$178.1238	$178.12	$178.10	$178.10
7 purchase totals =	$606.75		$665.4019	$665.39	$665.35	$665.50