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	$11.89	3.767%	$12.3379	$12.34	$12.35	$12.30
Purchase #2	$23.54	10.276%	$25.959	$25.96	$25.95	$26.00
Purchase #3	$164.26	6.651%	$175.1849	$175.18	$175.20	$175.20
Purchase #4	$137.83	4.179%	$143.5899	$143.59	$143.60	$143.60
Purchase #5	$59.86	4.302%	$62.4352	$62.44	$62.45	$62.40
Purchase #6	$88.71	12.611%	$99.8972	$99.90	$99.90	$99.90
Purchase #7	$34.25	5.620%	$36.1749	$36.17	$36.15	$36.20
7 purchase totals =	$520.34		$555.5790	$555.58	$555.60	$555.60