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	$143.27	5.747%	$151.5037	$151.50	$151.50	$151.50
Purchase #2	$46.31	9.176%	$50.5594	$50.56	$50.55	$50.60
Purchase #3	$171.70	4.718%	$179.8008	$179.80	$179.80	$179.80
Purchase #4	$215.27	11.443%	$239.9033	$239.90	$239.90	$239.90
Purchase #5	$203.71	4.110%	$212.0825	$212.08	$212.10	$212.10
Purchase #6	$81.45	10.445%	$89.9575	$89.96	$89.95	$90.00
Purchase #7	$45.37	13.793%	$51.6279	$51.63	$51.65	$51.60
7 purchase totals =	$907.08		$975.4351	$975.43	$975.45	$975.50