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	$33.35	9.444%	$36.4996	$36.50	$36.50	$36.50
Purchase #2	$218.91	13.675%	$248.8459	$248.85	$248.85	$248.80
Purchase #3	$31.76	12.401%	$35.6986	$35.70	$35.70	$35.70
Purchase #4	$84.45	6.646%	$90.0625	$90.06	$90.05	$90.10
Purchase #5	$25.60	6.298%	$27.2123	$27.21	$27.20	$27.20
Purchase #6	$14.87	5.407%	$15.674	$15.67	$15.65	$15.70
Purchase #7	$61.82	9.145%	$67.4734	$67.47	$67.45	$67.50
7 purchase totals =	$470.76		$521.4663	$521.46	$521.40	$521.50