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	$236.48	12.209%	$265.3518	$265.35	$265.35	$265.40
Purchase #2	$138.42	9.124%	$151.0494	$151.05	$151.05	$151.00
Purchase #3	$110.51	12.114%	$123.8972	$123.90	$123.90	$123.90
Purchase #4	$156.72	8.360%	$169.8218	$169.82	$169.80	$169.80
Purchase #5	$52.78	4.206%	$54.9999	$55.00	$55.00	$55.00
Purchase #6	$12.29	13.137%	$13.9045	$13.90	$13.90	$13.90
Purchase #7	$204.46	10.268%	$225.454	$225.45	$225.45	$225.50
7 purchase totals =	$911.66		$1,004.4786	$1,004.47	$1,004.45	$1,004.50