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	$87.56	4.319%	$91.3417	$91.34	$91.35	$91.30
Purchase #2	$152.26	7.272%	$163.3323	$163.33	$163.35	$163.30
Purchase #3	$71.83	9.866%	$78.9167	$78.92	$78.90	$78.90
Purchase #4	$198.48	7.288%	$212.9452	$212.95	$212.95	$212.90
Purchase #5	$169.86	11.616%	$189.5909	$189.59	$189.60	$189.60
Purchase #6	$132.76	11.840%	$148.4788	$148.48	$148.50	$148.50
Purchase #7	$93.66	12.621%	$105.4808	$105.48	$105.50	$105.50
7 purchase totals =	$906.41		$990.0864	$990.09	$990.15	$990.00