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	$16.87	10.612%	$18.6602	$18.66	$18.65	$18.70
Purchase #2	$59.70	4.463%	$62.3644	$62.36	$62.35	$62.40
Purchase #3	$98.69	9.868%	$108.4287	$108.43	$108.45	$108.40
Purchase #4	$131.92	9.863%	$144.9313	$144.93	$144.95	$144.90
Purchase #5	$18.34	10.274%	$20.2243	$20.22	$20.20	$20.20
Purchase #6	$88.50	11.438%	$98.6226	$98.62	$98.60	$98.60
Purchase #7	$34.39	9.227%	$37.5632	$37.56	$37.55	$37.60
7 purchase totals =	$448.41		$490.7947	$490.78	$490.75	$490.80