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	$140.70	11.430%	$156.782	$156.78	$156.80	$156.80
Purchase #2	$155.70	4.320%	$162.4262	$162.43	$162.45	$162.40
Purchase #3	$148.39	12.128%	$166.3867	$166.39	$166.40	$166.40
Purchase #4	$64.83	3.798%	$67.2922	$67.29	$67.30	$67.30
Purchase #5	$30.39	5.610%	$32.0949	$32.09	$32.10	$32.10
Purchase #6	$44.95	11.864%	$50.2829	$50.28	$50.30	$50.30
Purchase #7	$153.55	4.224%	$160.036	$160.04	$160.05	$160.00
7 purchase totals =	$738.51		$795.3009	$795.30	$795.40	$795.30