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	$13.71	10.751%	$15.184	$15.18	$15.20	$15.20
Purchase #2	$127.72	10.138%	$140.6683	$140.67	$140.65	$140.70
Purchase #3	$150.74	10.234%	$166.1667	$166.17	$166.15	$166.20
Purchase #4	$45.79	13.761%	$52.0912	$52.09	$52.10	$52.10
Purchase #5	$21.90	13.794%	$24.9209	$24.92	$24.90	$24.90
Purchase #6	$164.34	10.417%	$181.4593	$181.46	$181.45	$181.50
Purchase #7	$79.31	3.396%	$82.0034	$82.00	$82.00	$82.00
7 purchase totals =	$603.51		$662.4938	$662.49	$662.45	$662.60