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	$75.65	3.122%	$78.0118	$78.01	$78.00	$78.00
Purchase #2	$92.71	3.124%	$95.6063	$95.61	$95.60	$95.60
Purchase #3	$33.48	13.652%	$38.0507	$38.05	$38.05	$38.10
Purchase #4	$27.68	10.200%	$30.5034	$30.50	$30.50	$30.50
Purchase #5	$89.86	12.655%	$101.2318	$101.23	$101.25	$101.20
Purchase #6	$105.48	13.652%	$119.8801	$119.88	$119.90	$119.90
Purchase #7	$176.72	6.299%	$187.8516	$187.85	$187.85	$187.90
7 purchase totals =	$601.58		$651.1357	$651.13	$651.15	$651.20