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	$122.85	4.821%	$128.7726	$128.77	$128.75	$128.80
Purchase #2	$145.61	12.306%	$163.5288	$163.53	$163.55	$163.50
Purchase #3	$97.87	5.253%	$103.0111	$103.01	$103.00	$103.00
Purchase #4	$119.99	7.450%	$128.9293	$128.93	$128.95	$128.90
Purchase #5	$240.57	6.123%	$255.3001	$255.30	$255.30	$255.30
Purchase #6	$108.58	11.236%	$120.78	$120.78	$120.80	$120.80
Purchase #7	$106.83	4.139%	$111.2517	$111.25	$111.25	$111.30
7 purchase totals =	$942.30		$1,011.5736	$1,011.57	$1,011.60	$1,011.60