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	$89.49	8.265%	$96.8863	$96.89	$96.90	$96.90
Purchase #2	$128.87	9.396%	$140.9786	$140.98	$141.00	$141.00
Purchase #3	$250.54	10.744%	$277.458	$277.46	$277.45	$277.50
Purchase #4	$45.89	12.526%	$51.6382	$51.64	$51.65	$51.60
Purchase #5	$18.68	12.713%	$21.0548	$21.05	$21.05	$21.10
Purchase #6	$57.98	12.495%	$65.2246	$65.22	$65.20	$65.20
Purchase #7	$107.87	4.677%	$112.9151	$112.92	$112.90	$112.90
7 purchase totals =	$699.32		$766.1556	$766.16	$766.15	$766.20