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	$85.99	3.158%	$88.7056	$88.71	$88.70	$88.70
Purchase #2	$158.53	7.690%	$170.721	$170.72	$170.70	$170.70
Purchase #3	$19.29	6.752%	$20.5925	$20.59	$20.60	$20.60
Purchase #4	$194.34	4.660%	$203.3962	$203.40	$203.40	$203.40
Purchase #5	$172.49	4.305%	$179.9157	$179.92	$179.90	$179.90
Purchase #6	$71.60	9.811%	$78.6247	$78.62	$78.60	$78.60
Purchase #7	$63.67	6.141%	$67.58	$67.58	$67.60	$67.60
7 purchase totals =	$765.91		$809.5357	$809.54	$809.50	$809.50