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	$18.46	12.268%	$20.7247	$20.72	$20.70	$20.70
Purchase #2	$80.60	12.477%	$90.6565	$90.66	$90.65	$90.70
Purchase #3	$179.60	4.723%	$188.0825	$188.08	$188.10	$188.10
Purchase #4	$62.41	6.258%	$66.3156	$66.32	$66.30	$66.30
Purchase #5	$107.92	9.333%	$117.9922	$117.99	$118.00	$118.00
Purchase #6	$208.88	10.749%	$231.3325	$231.33	$231.35	$231.30
Purchase #7	$186.60	11.873%	$208.755	$208.76	$208.75	$208.80
7 purchase totals =	$844.47		$923.8590	$923.86	$923.85	$923.90