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	$103.72	13.462%	$117.6828	$117.68	$117.70	$117.70
Purchase #2	$38.72	6.753%	$41.3348	$41.33	$41.35	$41.30
Purchase #3	$52.44	11.481%	$58.4606	$58.46	$58.45	$58.50
Purchase #4	$118.74	3.682%	$123.112	$123.11	$123.10	$123.10
Purchase #5	$43.81	4.492%	$45.7779	$45.78	$45.80	$45.80
Purchase #6	$62.65	3.471%	$64.8246	$64.82	$64.80	$64.80
Purchase #7	$196.82	10.304%	$217.1003	$217.10	$217.10	$217.10
7 purchase totals =	$616.90		$668.2930	$668.28	$668.30	$668.30