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	$115.86	13.164%	$131.1118	$131.11	$131.10	$131.10
Purchase #2	$157.72	4.433%	$164.7117	$164.71	$164.70	$164.70
Purchase #3	$124.69	9.568%	$136.6203	$136.62	$136.60	$136.60
Purchase #4	$6.36	7.182%	$6.8168	$6.82	$6.80	$6.80
Purchase #5	$118.36	8.523%	$128.4478	$128.45	$128.45	$128.40
Purchase #6	$56.76	4.568%	$59.3528	$59.35	$59.35	$59.40
Purchase #7	$125.47	5.520%	$132.3959	$132.40	$132.40	$132.40
7 purchase totals =	$705.22		$759.4571	$759.46	$759.40	$759.40