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	$155.62	8.444%	$168.7606	$168.76	$168.75	$168.80
Purchase #2	$182.71	7.553%	$196.5101	$196.51	$196.50	$196.50
Purchase #3	$34.26	3.587%	$35.4889	$35.49	$35.50	$35.50
Purchase #4	$18.99	11.823%	$21.2352	$21.24	$21.25	$21.20
Purchase #5	$131.59	5.874%	$139.3196	$139.32	$139.30	$139.30
Purchase #6	$24.55	10.646%	$27.1636	$27.16	$27.15	$27.20
Purchase #7	$84.62	6.143%	$89.8182	$89.82	$89.80	$89.80
7 purchase totals =	$632.34		$678.2962	$678.30	$678.25	$678.30