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	$144.77	9.680%	$158.7837	$158.78	$158.80	$158.80
Purchase #2	$54.95	4.647%	$57.5035	$57.50	$57.50	$57.50
Purchase #3	$84.87	13.763%	$96.5507	$96.55	$96.55	$96.60
Purchase #4	$163.40	13.706%	$185.7956	$185.80	$185.80	$185.80
Purchase #5	$65.82	6.370%	$70.0127	$70.01	$70.00	$70.00
Purchase #6	$108.72	3.809%	$112.8611	$112.86	$112.85	$112.90
Purchase #7	$16.25	11.391%	$18.101	$18.10	$18.10	$18.10
7 purchase totals =	$638.78		$699.6083	$699.60	$699.60	$699.70