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	$124.66	11.871%	$139.4584	$139.46	$139.45	$139.50
Purchase #2	$135.25	12.681%	$152.4011	$152.40	$152.40	$152.40
Purchase #3	$134.68	13.504%	$152.8672	$152.87	$152.85	$152.90
Purchase #4	$163.69	6.343%	$174.0729	$174.07	$174.05	$174.10
Purchase #5	$166.76	9.393%	$182.4238	$182.42	$182.40	$182.40
Purchase #6	$66.44	8.445%	$72.0509	$72.05	$72.05	$72.10
Purchase #7	$52.34	8.392%	$56.7324	$56.73	$56.75	$56.70
7 purchase totals =	$843.82		$930.0067	$930.00	$929.95	$930.10