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	$178.38	5.573%	$188.3211	$188.32	$188.30	$188.30
Purchase #2	$190.95	6.517%	$203.3942	$203.39	$203.40	$203.40
Purchase #3	$71.58	9.602%	$78.4531	$78.45	$78.45	$78.50
Purchase #4	$103.67	10.112%	$114.1531	$114.15	$114.15	$114.20
Purchase #5	$152.37	4.637%	$159.4354	$159.44	$159.45	$159.40
Purchase #6	$52.45	6.648%	$55.9369	$55.94	$55.95	$55.90
Purchase #7	$148.45	5.288%	$156.3	$156.30	$156.30	$156.30
7 purchase totals =	$897.85		$955.9938	$955.99	$956.00	$956.00