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	$124.62	13.873%	$141.9085	$141.91	$141.90	$141.90
Purchase #2	$66.80	3.768%	$69.317	$69.32	$69.30	$69.30
Purchase #3	$9.44	10.843%	$10.4636	$10.46	$10.45	$10.50
Purchase #4	$63.89	12.493%	$71.8718	$71.87	$71.85	$71.90
Purchase #5	$117.63	12.679%	$132.5443	$132.54	$132.55	$132.50
Purchase #6	$92.27	6.457%	$98.2279	$98.23	$98.25	$98.20
Purchase #7	$133.68	5.770%	$141.3933	$141.39	$141.40	$141.40
7 purchase totals =	$608.33		$665.7264	$665.72	$665.70	$665.70