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	$13.79	12.155%	$15.4662	$15.47	$15.45	$15.50
Purchase #2	$142.58	10.785%	$157.9573	$157.96	$157.95	$158.00
Purchase #3	$192.27	3.815%	$199.6051	$199.61	$199.60	$199.60
Purchase #4	$112.61	13.506%	$127.8191	$127.82	$127.80	$127.80
Purchase #5	$149.38	10.648%	$165.286	$165.29	$165.30	$165.30
Purchase #6	$135.48	8.860%	$147.4835	$147.48	$147.50	$147.50
Purchase #7	$176.25	9.850%	$193.6106	$193.61	$193.60	$193.60
7 purchase totals =	$922.36		$1,007.2278	$1,007.24	$1,007.20	$1,007.30