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	$180.83	8.716%	$196.5911	$196.59	$196.60	$196.60
Purchase #2	$132.98	13.502%	$150.935	$150.94	$150.95	$150.90
Purchase #3	$86.53	4.346%	$90.2906	$90.29	$90.30	$90.30
Purchase #4	$87.62	9.225%	$95.7029	$95.70	$95.70	$95.70
Purchase #5	$110.93	12.663%	$124.9771	$124.98	$125.00	$125.00
Purchase #6	$12.43	8.867%	$13.5322	$13.53	$13.55	$13.50
Purchase #7	$90.80	9.581%	$99.4995	$99.50	$99.50	$99.50
7 purchase totals =	$702.12		$771.5284	$771.53	$771.60	$771.50