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	$86.66	3.744%	$89.9046	$89.90	$89.90	$89.90
Purchase #2	$141.99	12.228%	$159.3525	$159.35	$159.35	$159.40
Purchase #3	$92.99	5.326%	$97.9426	$97.94	$97.95	$97.90
Purchase #4	$95.31	4.646%	$99.7381	$99.74	$99.75	$99.70
Purchase #5	$51.43	3.544%	$53.2527	$53.25	$53.25	$53.30
Purchase #6	$213.32	12.506%	$239.9978	$240.00	$240.00	$240.00
Purchase #7	$240.42	6.333%	$255.6458	$255.65	$255.65	$255.60
7 purchase totals =	$922.12		$995.8341	$995.83	$995.85	$995.80