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	$59.54	12.614%	$67.0504	$67.05	$67.05	$67.10
Purchase #2	$147.25	9.274%	$160.906	$160.91	$160.90	$160.90
Purchase #3	$52.34	5.296%	$55.1119	$55.11	$55.10	$55.10
Purchase #4	$43.54	11.587%	$48.585	$48.59	$48.60	$48.60
Purchase #5	$194.97	7.109%	$208.8304	$208.83	$208.85	$208.80
Purchase #6	$121.44	7.497%	$130.5444	$130.54	$130.55	$130.50
Purchase #7	$19.92	9.429%	$21.7983	$21.80	$21.80	$21.80
7 purchase totals =	$639.00		$692.8264	$692.83	$692.85	$692.80