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	$63.32	11.600%	$70.6651	$70.67	$70.65	$70.70
Purchase #2	$231.87	12.285%	$260.3552	$260.36	$260.35	$260.40
Purchase #3	$119.44	9.196%	$130.4237	$130.42	$130.40	$130.40
Purchase #4	$80.38	12.584%	$90.495	$90.50	$90.50	$90.50
Purchase #5	$92.49	7.872%	$99.7708	$99.77	$99.75	$99.80
Purchase #6	$136.61	13.787%	$155.4444	$155.44	$155.45	$155.40
Purchase #7	$86.51	6.493%	$92.1271	$92.13	$92.15	$92.10
7 purchase totals =	$810.62		$899.2813	$899.29	$899.25	$899.30