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	$81.73	9.670%	$89.6333	$89.63	$89.65	$89.60
Purchase #2	$245.84	11.801%	$274.8516	$274.85	$274.85	$274.90
Purchase #3	$19.60	12.213%	$21.9937	$21.99	$22.00	$22.00
Purchase #4	$106.61	4.447%	$111.3509	$111.35	$111.35	$111.40
Purchase #5	$61.40	11.738%	$68.6071	$68.61	$68.60	$68.60
Purchase #6	$241.78	7.342%	$259.5315	$259.53	$259.55	$259.50
Purchase #7	$216.84	10.632%	$239.8944	$239.89	$239.90	$239.90
7 purchase totals =	$973.80		$1,065.8625	$1,065.85	$1,065.90	$1,065.90