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	$233.85	12.250%	$262.4966	$262.50	$262.50	$262.50
Purchase #2	$188.52	6.190%	$200.1894	$200.19	$200.20	$200.20
Purchase #3	$182.93	8.528%	$198.5303	$198.53	$198.55	$198.50
Purchase #4	$152.59	10.735%	$168.9705	$168.97	$168.95	$169.00
Purchase #5	$104.46	4.186%	$108.8327	$108.83	$108.85	$108.80
Purchase #6	$140.29	4.300%	$146.3225	$146.32	$146.30	$146.30
Purchase #7	$195.31	4.172%	$203.4583	$203.46	$203.45	$203.50
7 purchase totals =	$1,197.95		$1,288.8003	$1,288.80	$1,288.80	$1,288.80