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	$204.59	8.734%	$222.4589	$222.46	$222.45	$222.50
Purchase #2	$155.67	6.469%	$165.7403	$165.74	$165.75	$165.70
Purchase #3	$191.95	7.493%	$206.3328	$206.33	$206.35	$206.30
Purchase #4	$18.75	12.719%	$21.1348	$21.13	$21.15	$21.10
Purchase #5	$58.85	10.253%	$64.8839	$64.88	$64.90	$64.90
Purchase #6	$97.92	5.365%	$103.1734	$103.17	$103.15	$103.20
Purchase #7	$241.93	13.368%	$274.2712	$274.27	$274.25	$274.30
7 purchase totals =	$969.66		$1,057.9953	$1,057.98	$1,058.00	$1,058.00