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	$101.82	6.658%	$108.5992	$108.60	$108.60	$108.60
Purchase #2	$183.55	3.567%	$190.0972	$190.10	$190.10	$190.10
Purchase #3	$71.54	7.481%	$76.8919	$76.89	$76.90	$76.90
Purchase #4	$140.83	5.123%	$148.0447	$148.04	$148.05	$148.00
Purchase #5	$81.71	8.369%	$88.5483	$88.55	$88.55	$88.50
Purchase #6	$114.98	4.839%	$120.5439	$120.54	$120.55	$120.50
Purchase #7	$240.87	11.226%	$267.9101	$267.91	$267.90	$267.90
7 purchase totals =	$935.30		$1,000.6353	$1,000.63	$1,000.65	$1,000.50