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	$180.26	5.367%	$189.9346	$189.93	$189.95	$189.90
Purchase #2	$117.89	4.404%	$123.0819	$123.08	$123.10	$123.10
Purchase #3	$19.55	4.393%	$20.4088	$20.41	$20.40	$20.40
Purchase #4	$29.32	5.828%	$31.0288	$31.03	$31.05	$31.00
Purchase #5	$164.95	6.558%	$175.7674	$175.77	$175.75	$175.80
Purchase #6	$97.93	11.721%	$109.4084	$109.41	$109.40	$109.40
Purchase #7	$17.54	4.509%	$18.3309	$18.33	$18.35	$18.30
7 purchase totals =	$627.44		$667.9608	$667.96	$668.00	$667.90