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	$47.96	9.864%	$52.6908	$52.69	$52.70	$52.70
Purchase #2	$63.31	6.746%	$67.5809	$67.58	$67.60	$67.60
Purchase #3	$105.43	6.678%	$112.4706	$112.47	$112.45	$112.50
Purchase #4	$250.80	12.108%	$281.1669	$281.17	$281.15	$281.20
Purchase #5	$87.38	13.583%	$99.2488	$99.25	$99.25	$99.20
Purchase #6	$160.85	3.103%	$165.8412	$165.84	$165.85	$165.80
Purchase #7	$55.93	7.350%	$60.0409	$60.04	$60.05	$60.00
7 purchase totals =	$771.66		$839.0401	$839.04	$839.05	$839.00