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	$24.91	10.619%	$27.5552	$27.56	$27.55	$27.60
Purchase #2	$58.76	8.112%	$63.5266	$63.53	$63.55	$63.50
Purchase #3	$89.69	6.566%	$95.579	$95.58	$95.60	$95.60
Purchase #4	$184.40	6.708%	$196.7696	$196.77	$196.75	$196.80
Purchase #5	$72.64	4.692%	$76.0483	$76.05	$76.05	$76.00
Purchase #6	$130.81	10.779%	$144.91	$144.91	$144.90	$144.90
Purchase #7	$30.71	7.708%	$33.0771	$33.08	$33.10	$33.10
7 purchase totals =	$591.92		$637.4658	$637.48	$637.50	$637.50