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	$152.97	3.431%	$158.2184	$158.22	$158.20	$158.20
Purchase #2	$37.37	9.181%	$40.8009	$40.80	$40.80	$40.80
Purchase #3	$150.29	4.192%	$156.5902	$156.59	$156.60	$156.60
Purchase #4	$150.98	7.442%	$162.2159	$162.22	$162.20	$162.20
Purchase #5	$164.26	7.451%	$176.499	$176.50	$176.50	$176.50
Purchase #6	$229.28	4.459%	$239.5036	$239.50	$239.50	$239.50
Purchase #7	$52.94	5.573%	$55.8903	$55.89	$55.90	$55.90
7 purchase totals =	$938.09		$989.7183	$989.72	$989.70	$989.70