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	$99.83	11.788%	$111.598	$111.60	$111.60	$111.60
Purchase #2	$112.61	4.379%	$117.5412	$117.54	$117.55	$117.50
Purchase #3	$97.73	8.223%	$105.7663	$105.77	$105.75	$105.80
Purchase #4	$240.64	9.122%	$262.5912	$262.59	$262.60	$262.60
Purchase #5	$229.60	13.108%	$259.696	$259.70	$259.70	$259.70
Purchase #6	$77.94	10.777%	$86.3396	$86.34	$86.35	$86.30
Purchase #7	$32.51	10.796%	$36.0198	$36.02	$36.00	$36.00
7 purchase totals =	$890.86		$979.5521	$979.56	$979.55	$979.50