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	$138.92	3.431%	$143.6863	$143.69	$143.70	$143.70
Purchase #2	$63.38	13.443%	$71.9002	$71.90	$71.90	$71.90
Purchase #3	$126.38	12.296%	$141.9197	$141.92	$141.90	$141.90
Purchase #4	$72.83	11.151%	$80.9513	$80.95	$80.95	$81.00
Purchase #5	$117.97	7.616%	$126.9546	$126.95	$126.95	$127.00
Purchase #6	$72.72	4.195%	$75.7706	$75.77	$75.75	$75.80
Purchase #7	$135.59	12.528%	$152.5767	$152.58	$152.60	$152.60
7 purchase totals =	$727.79		$793.7594	$793.76	$793.75	$793.90