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	$43.94	13.586%	$49.9097	$49.91	$49.90	$49.90
Purchase #2	$64.33	5.443%	$67.8315	$67.83	$67.85	$67.80
Purchase #3	$92.86	8.847%	$101.0753	$101.08	$101.10	$101.10
Purchase #4	$143.54	3.507%	$148.5739	$148.57	$148.55	$148.60
Purchase #5	$240.70	9.437%	$263.4149	$263.41	$263.40	$263.40
Purchase #6	$185.40	3.846%	$192.5305	$192.53	$192.55	$192.50
Purchase #7	$196.27	10.606%	$217.0864	$217.09	$217.10	$217.10
7 purchase totals =	$967.04		$1,040.4222	$1,040.42	$1,040.45	$1,040.40