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	$138.45	3.468%	$143.2514	$143.25	$143.25	$143.30
Purchase #2	$240.79	5.643%	$254.3778	$254.38	$254.40	$254.40
Purchase #3	$144.31	12.537%	$162.4021	$162.40	$162.40	$162.40
Purchase #4	$157.48	7.705%	$169.6138	$169.61	$169.60	$169.60
Purchase #5	$64.67	11.555%	$72.1426	$72.14	$72.15	$72.10
Purchase #6	$233.79	3.672%	$242.3748	$242.37	$242.35	$242.40
Purchase #7	$231.46	3.690%	$240.0009	$240.00	$240.00	$240.00
7 purchase totals =	$1,210.95		$1,284.1634	$1,284.15	$1,284.15	$1,284.20