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	$51.40	11.509%	$57.3156	$57.32	$57.30	$57.30
Purchase #2	$162.32	10.630%	$179.5746	$179.57	$179.55	$179.60
Purchase #3	$188.32	13.396%	$213.5473	$213.55	$213.55	$213.50
Purchase #4	$210.97	9.667%	$231.3645	$231.36	$231.35	$231.40
Purchase #5	$166.49	11.218%	$185.1668	$185.17	$185.15	$185.20
Purchase #6	$36.34	12.112%	$40.7415	$40.74	$40.75	$40.70
Purchase #7	$91.82	6.669%	$97.9435	$97.94	$97.95	$97.90
7 purchase totals =	$907.66		$1,005.6538	$1,005.65	$1,005.60	$1,005.60