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	$97.76	12.206%	$109.6926	$109.69	$109.70	$109.70
Purchase #2	$109.36	4.679%	$114.477	$114.48	$114.50	$114.50
Purchase #3	$34.77	11.661%	$38.8245	$38.82	$38.80	$38.80
Purchase #4	$147.79	6.166%	$156.9027	$156.90	$156.90	$156.90
Purchase #5	$11.62	10.312%	$12.8183	$12.82	$12.80	$12.80
Purchase #6	$151.41	9.680%	$166.0665	$166.07	$166.05	$166.10
Purchase #7	$50.63	12.264%	$56.8393	$56.84	$56.85	$56.80
7 purchase totals =	$603.34		$655.6209	$655.62	$655.60	$655.60