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	$24.61	5.219%	$25.8944	$25.89	$25.90	$25.90
Purchase #2	$76.75	7.296%	$82.3497	$82.35	$82.35	$82.30
Purchase #3	$18.51	9.140%	$20.2018	$20.20	$20.20	$20.20
Purchase #4	$187.51	5.687%	$198.1737	$198.17	$198.15	$198.20
Purchase #5	$26.79	3.182%	$27.6425	$27.64	$27.65	$27.60
Purchase #6	$84.72	5.704%	$89.5524	$89.55	$89.55	$89.60
Purchase #7	$224.75	13.327%	$254.7024	$254.70	$254.70	$254.70
7 purchase totals =	$643.64		$698.5169	$698.50	$698.50	$698.50