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	$112.61	6.768%	$120.2314	$120.23	$120.25	$120.20
Purchase #2	$229.25	6.278%	$243.6423	$243.64	$243.65	$243.60
Purchase #3	$121.27	8.611%	$131.7126	$131.71	$131.70	$131.70
Purchase #4	$231.39	10.243%	$255.0913	$255.09	$255.10	$255.10
Purchase #5	$173.45	10.338%	$191.3813	$191.38	$191.40	$191.40
Purchase #6	$58.55	5.773%	$61.9301	$61.93	$61.95	$61.90
Purchase #7	$177.58	5.476%	$187.3043	$187.30	$187.30	$187.30
7 purchase totals =	$1,104.10		$1,191.2933	$1,191.28	$1,191.35	$1,191.20