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	$233.64	9.306%	$255.3825	$255.38	$255.40	$255.40
Purchase #2	$121.89	9.319%	$133.2489	$133.25	$133.25	$133.20
Purchase #3	$158.38	7.784%	$170.7083	$170.71	$170.70	$170.70
Purchase #4	$247.59	7.839%	$266.9986	$267.00	$267.00	$267.00
Purchase #5	$50.82	9.428%	$55.6113	$55.61	$55.60	$55.60
Purchase #6	$161.75	10.835%	$179.2756	$179.28	$179.30	$179.30
Purchase #7	$58.83	6.175%	$62.4628	$62.46	$62.45	$62.50
7 purchase totals =	$1,032.90		$1,123.6880	$1,123.69	$1,123.70	$1,123.70