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	$179.58	5.859%	$190.1016	$190.10	$190.10	$190.10
Purchase #2	$227.39	12.345%	$255.4613	$255.46	$255.45	$255.50
Purchase #3	$245.37	13.696%	$278.9759	$278.98	$279.00	$279.00
Purchase #4	$215.47	10.372%	$237.8185	$237.82	$237.80	$237.80
Purchase #5	$208.35	12.422%	$234.2312	$234.23	$234.25	$234.20
Purchase #6	$100.77	13.644%	$114.5191	$114.52	$114.50	$114.50
Purchase #7	$246.37	5.211%	$259.2083	$259.21	$259.20	$259.20
7 purchase totals =	$1,423.30		$1,570.3159	$1,570.32	$1,570.30	$1,570.30