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	$131.85	12.425%	$148.2324	$148.23	$148.25	$148.20
Purchase #2	$110.39	3.788%	$114.5716	$114.57	$114.55	$114.60
Purchase #3	$166.79	13.249%	$188.888	$188.89	$188.90	$188.90
Purchase #4	$70.66	13.553%	$80.2365	$80.24	$80.25	$80.20
Purchase #5	$35.47	5.295%	$37.3481	$37.35	$37.35	$37.30
Purchase #6	$196.43	13.244%	$222.4452	$222.45	$222.45	$222.40
Purchase #7	$46.56	3.813%	$48.3353	$48.34	$48.35	$48.30
7 purchase totals =	$758.15		$840.0571	$840.07	$840.10	$839.90