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	$11.96	9.795%	$13.1315	$13.13	$13.15	$13.10
Purchase #2	$129.57	8.722%	$140.8711	$140.87	$140.85	$140.90
Purchase #3	$48.28	7.532%	$51.9164	$51.92	$51.90	$51.90
Purchase #4	$55.29	12.834%	$62.3859	$62.39	$62.40	$62.40
Purchase #5	$78.90	13.695%	$89.7054	$89.71	$89.70	$89.70
Purchase #6	$217.47	11.520%	$242.5225	$242.52	$242.50	$242.50
Purchase #7	$49.44	8.362%	$53.5742	$53.57	$53.55	$53.60
7 purchase totals =	$590.91		$654.1070	$654.11	$654.05	$654.10