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	$159.51	6.284%	$169.5336	$169.53	$169.55	$169.50
Purchase #2	$178.76	11.752%	$199.7679	$199.77	$199.75	$199.80
Purchase #3	$69.77	5.554%	$73.645	$73.65	$73.65	$73.60
Purchase #4	$85.30	3.169%	$88.0032	$88.00	$88.00	$88.00
Purchase #5	$99.66	12.851%	$112.4673	$112.47	$112.45	$112.50
Purchase #6	$85.45	8.287%	$92.5312	$92.53	$92.55	$92.50
Purchase #7	$39.49	7.777%	$42.5611	$42.56	$42.55	$42.60
7 purchase totals =	$717.94		$778.5093	$778.51	$778.50	$778.50