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	$98.56	11.214%	$109.6125	$109.61	$109.60	$109.60
Purchase #2	$139.95	3.330%	$144.6103	$144.61	$144.60	$144.60
Purchase #3	$199.60	5.493%	$210.564	$210.56	$210.55	$210.60
Purchase #4	$53.32	10.652%	$58.9996	$59.00	$59.00	$59.00
Purchase #5	$109.78	11.698%	$122.6221	$122.62	$122.60	$122.60
Purchase #6	$245.64	8.743%	$267.1163	$267.12	$267.10	$267.10
Purchase #7	$70.58	9.116%	$77.0141	$77.01	$77.00	$77.00
7 purchase totals =	$917.43		$990.5389	$990.53	$990.45	$990.50