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	$100.65	12.780%	$113.5131	$113.51	$113.50	$113.50
Purchase #2	$90.52	11.516%	$100.9443	$100.94	$100.95	$100.90
Purchase #3	$248.27	4.782%	$260.1423	$260.14	$260.15	$260.10
Purchase #4	$27.47	9.459%	$30.0684	$30.07	$30.05	$30.10
Purchase #5	$172.83	5.526%	$182.3806	$182.38	$182.40	$182.40
Purchase #6	$196.53	8.731%	$213.689	$213.69	$213.70	$213.70
Purchase #7	$245.64	13.671%	$279.2214	$279.22	$279.20	$279.20
7 purchase totals =	$1,081.91		$1,179.9591	$1,179.95	$1,179.95	$1,179.90