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	$226.61	13.826%	$257.9411	$257.94	$257.95	$257.90
Purchase #2	$95.52	5.115%	$100.4058	$100.41	$100.40	$100.40
Purchase #3	$154.44	11.380%	$172.0153	$172.02	$172.00	$172.00
Purchase #4	$162.48	10.421%	$179.412	$179.41	$179.40	$179.40
Purchase #5	$166.48	6.169%	$176.7502	$176.75	$176.75	$176.80
Purchase #6	$81.64	13.836%	$92.9357	$92.94	$92.95	$92.90
Purchase #7	$88.88	7.576%	$95.6135	$95.61	$95.60	$95.60
7 purchase totals =	$976.05		$1,075.0736	$1,075.08	$1,075.05	$1,075.00