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	$165.90	13.691%	$188.6134	$188.61	$188.60	$188.60
Purchase #2	$83.71	3.366%	$86.5277	$86.53	$86.55	$86.50
Purchase #3	$125.86	11.147%	$139.8896	$139.89	$139.90	$139.90
Purchase #4	$59.77	13.506%	$67.8425	$67.84	$67.85	$67.80
Purchase #5	$173.54	5.761%	$183.5376	$183.54	$183.55	$183.50
Purchase #6	$19.78	3.256%	$20.424	$20.42	$20.40	$20.40
Purchase #7	$10.96	5.680%	$11.5825	$11.58	$11.60	$11.60
7 purchase totals =	$639.52		$698.4173	$698.41	$698.45	$698.30