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	$138.88	12.341%	$156.0192	$156.02	$156.00	$156.00
Purchase #2	$153.59	3.215%	$158.5279	$158.53	$158.55	$158.50
Purchase #3	$109.64	5.748%	$115.9421	$115.94	$115.95	$115.90
Purchase #4	$205.87	6.758%	$219.7827	$219.78	$219.80	$219.80
Purchase #5	$133.91	9.273%	$146.3275	$146.33	$146.35	$146.30
Purchase #6	$98.93	10.749%	$109.564	$109.56	$109.55	$109.60
Purchase #7	$119.71	4.176%	$124.7091	$124.71	$124.70	$124.70
7 purchase totals =	$960.53		$1,030.8725	$1,030.87	$1,030.90	$1,030.80