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	$133.59	10.655%	$147.824	$147.82	$147.80	$147.80
Purchase #2	$20.48	3.850%	$21.2685	$21.27	$21.25	$21.30
Purchase #3	$80.41	10.849%	$89.1337	$89.13	$89.15	$89.10
Purchase #4	$65.63	10.804%	$72.7207	$72.72	$72.70	$72.70
Purchase #5	$209.91	9.601%	$230.0635	$230.06	$230.05	$230.10
Purchase #6	$12.77	5.864%	$13.5188	$13.52	$13.50	$13.50
Purchase #7	$160.45	6.710%	$171.2162	$171.22	$171.20	$171.20
7 purchase totals =	$683.24		$745.7454	$745.74	$745.65	$745.70