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	$79.85	11.265%	$88.8451	$88.85	$88.85	$88.80
Purchase #2	$47.59	3.679%	$49.3408	$49.34	$49.35	$49.30
Purchase #3	$109.84	6.387%	$116.8555	$116.86	$116.85	$116.90
Purchase #4	$36.54	10.273%	$40.2938	$40.29	$40.30	$40.30
Purchase #5	$228.27	11.265%	$253.9846	$253.98	$254.00	$254.00
Purchase #6	$44.89	8.254%	$48.5952	$48.60	$48.60	$48.60
Purchase #7	$64.47	11.276%	$71.7396	$71.74	$71.75	$71.70
7 purchase totals =	$611.45		$669.6546	$669.66	$669.70	$669.60