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	$116.59	4.525%	$121.8657	$121.87	$121.85	$121.90
Purchase #2	$27.96	12.500%	$31.455	$31.46	$31.45	$31.50
Purchase #3	$88.27	10.836%	$97.8349	$97.83	$97.85	$97.80
Purchase #4	$108.57	3.543%	$112.4166	$112.42	$112.40	$112.40
Purchase #5	$34.31	9.463%	$37.5568	$37.56	$37.55	$37.60
Purchase #6	$204.28	10.311%	$225.3433	$225.34	$225.35	$225.30
Purchase #7	$18.89	9.355%	$20.6572	$20.66	$20.65	$20.70
7 purchase totals =	$598.87		$647.1295	$647.14	$647.10	$647.20