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	$132.45	13.858%	$150.8049	$150.80	$150.80	$150.80
Purchase #2	$85.59	4.639%	$89.5605	$89.56	$89.55	$89.60
Purchase #3	$190.89	13.312%	$216.3013	$216.30	$216.30	$216.30
Purchase #4	$208.32	12.540%	$234.4433	$234.44	$234.45	$234.40
Purchase #5	$117.89	11.240%	$131.1408	$131.14	$131.15	$131.10
Purchase #6	$58.31	3.247%	$60.2033	$60.20	$60.20	$60.20
Purchase #7	$84.60	10.658%	$93.6167	$93.62	$93.60	$93.60
7 purchase totals =	$878.05		$976.0708	$976.06	$976.05	$976.00