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	$20.67	10.800%	$22.9024	$22.90	$22.90	$22.90
Purchase #2	$146.45	13.584%	$166.3438	$166.34	$166.35	$166.30
Purchase #3	$161.27	13.458%	$182.9737	$182.97	$182.95	$183.00
Purchase #4	$174.37	3.500%	$180.473	$180.47	$180.45	$180.50
Purchase #5	$77.75	6.683%	$82.946	$82.95	$82.95	$82.90
Purchase #6	$245.52	4.796%	$257.2951	$257.30	$257.30	$257.30
Purchase #7	$190.70	10.614%	$210.9409	$210.94	$210.95	$210.90
7 purchase totals =	$1,016.73		$1,103.8749	$1,103.87	$1,103.85	$1,103.80