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	$16.56	11.807%	$18.5152	$18.52	$18.50	$18.50
Purchase #2	$187.53	13.617%	$213.066	$213.07	$213.05	$213.10
Purchase #3	$138.42	7.772%	$149.178	$149.18	$149.20	$149.20
Purchase #4	$83.48	8.685%	$90.7302	$90.73	$90.75	$90.70
Purchase #5	$96.62	12.120%	$108.3303	$108.33	$108.35	$108.30
Purchase #6	$15.89	13.327%	$18.0077	$18.01	$18.00	$18.00
Purchase #7	$86.46	4.529%	$90.3758	$90.38	$90.40	$90.40
7 purchase totals =	$624.96		$688.2032	$688.22	$688.25	$688.20