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	$217.90	8.481%	$236.3801	$236.38	$236.40	$236.40
Purchase #2	$179.49	3.628%	$186.0019	$186.00	$186.00	$186.00
Purchase #3	$227.27	7.788%	$244.9698	$244.97	$244.95	$245.00
Purchase #4	$243.59	4.816%	$255.3213	$255.32	$255.30	$255.30
Purchase #5	$240.54	6.771%	$256.827	$256.83	$256.85	$256.80
Purchase #6	$136.82	3.262%	$141.2831	$141.28	$141.30	$141.30
Purchase #7	$115.71	3.521%	$119.7841	$119.78	$119.80	$119.80
7 purchase totals =	$1,361.32		$1,440.5673	$1,440.56	$1,440.60	$1,440.60