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	$140.90	6.824%	$150.515	$150.52	$150.50	$150.50
Purchase #2	$111.76	3.400%	$115.5598	$115.56	$115.55	$115.60
Purchase #3	$12.79	13.565%	$14.525	$14.53	$14.55	$14.50
Purchase #4	$36.32	11.742%	$40.5847	$40.58	$40.60	$40.60
Purchase #5	$134.58	3.395%	$139.149	$139.15	$139.15	$139.10
Purchase #6	$28.46	4.386%	$29.7083	$29.71	$29.70	$29.70
Purchase #7	$115.99	6.414%	$123.4296	$123.43	$123.45	$123.40
7 purchase totals =	$580.80		$613.4714	$613.48	$613.50	$613.40