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	$79.81	12.632%	$89.8916	$89.89	$89.90	$89.90
Purchase #2	$29.74	8.166%	$32.1686	$32.17	$32.15	$32.20
Purchase #3	$112.99	4.403%	$117.9649	$117.96	$117.95	$118.00
Purchase #4	$199.90	6.726%	$213.3453	$213.35	$213.35	$213.30
Purchase #5	$67.60	11.702%	$75.5106	$75.51	$75.50	$75.50
Purchase #6	$162.56	10.451%	$179.5491	$179.55	$179.55	$179.50
Purchase #7	$195.56	4.856%	$205.0564	$205.06	$205.05	$205.10
7 purchase totals =	$848.16		$913.4865	$913.49	$913.45	$913.50