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	$12.33	8.467%	$13.374	$13.37	$13.35	$13.40
Purchase #2	$19.61	7.146%	$21.0113	$21.01	$21.00	$21.00
Purchase #3	$143.45	11.786%	$160.357	$160.36	$160.35	$160.40
Purchase #4	$213.61	4.616%	$223.4702	$223.47	$223.45	$223.50
Purchase #5	$151.81	3.789%	$157.5621	$157.56	$157.55	$157.60
Purchase #6	$69.54	12.372%	$78.1435	$78.14	$78.15	$78.10
Purchase #7	$40.30	7.802%	$43.4442	$43.44	$43.45	$43.40
7 purchase totals =	$650.65		$697.3623	$697.35	$697.30	$697.40