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	$76.97	5.134%	$80.9216	$80.92	$80.90	$80.90
Purchase #2	$62.36	6.233%	$66.2469	$66.25	$66.25	$66.20
Purchase #3	$237.39	4.528%	$248.139	$248.14	$248.15	$248.10
Purchase #4	$29.82	7.741%	$32.1284	$32.13	$32.15	$32.10
Purchase #5	$81.29	12.389%	$91.361	$91.36	$91.35	$91.40
Purchase #6	$157.34	13.410%	$178.4393	$178.44	$178.45	$178.40
Purchase #7	$156.65	10.382%	$172.9134	$172.91	$172.90	$172.90
7 purchase totals =	$801.82		$870.1496	$870.15	$870.15	$870.00