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	$63.27	5.348%	$66.6537	$66.65	$66.65	$66.70
Purchase #2	$95.29	8.744%	$103.6222	$103.62	$103.60	$103.60
Purchase #3	$179.83	6.611%	$191.7186	$191.72	$191.70	$191.70
Purchase #4	$127.72	12.637%	$143.86	$143.86	$143.85	$143.90
Purchase #5	$140.66	11.566%	$156.9287	$156.93	$156.95	$156.90
Purchase #6	$95.97	7.343%	$103.0171	$103.02	$103.00	$103.00
Purchase #7	$161.63	11.589%	$180.3613	$180.36	$180.35	$180.40
7 purchase totals =	$864.37		$946.1616	$946.16	$946.10	$946.20