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	$42.91	4.203%	$44.7135	$44.71	$44.70	$44.70
Purchase #2	$140.64	11.332%	$156.5773	$156.58	$156.60	$156.60
Purchase #3	$41.83	4.535%	$43.727	$43.73	$43.75	$43.70
Purchase #4	$227.51	12.695%	$256.3924	$256.39	$256.40	$256.40
Purchase #5	$132.37	3.573%	$137.0996	$137.10	$137.10	$137.10
Purchase #6	$111.25	13.361%	$126.1141	$126.11	$126.10	$126.10
Purchase #7	$53.26	11.823%	$59.5569	$59.56	$59.55	$59.60
7 purchase totals =	$749.77		$824.1808	$824.18	$824.20	$824.20