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	$134.67	5.378%	$141.9126	$141.91	$141.90	$141.90
Purchase #2	$177.90	11.600%	$198.5364	$198.54	$198.55	$198.50
Purchase #3	$248.76	3.298%	$256.9641	$256.96	$256.95	$257.00
Purchase #4	$71.89	12.873%	$81.1444	$81.14	$81.15	$81.10
Purchase #5	$234.88	13.202%	$265.8889	$265.89	$265.90	$265.90
Purchase #6	$60.70	6.237%	$64.4859	$64.49	$64.50	$64.50
Purchase #7	$46.68	3.648%	$48.3829	$48.38	$48.40	$48.40
7 purchase totals =	$975.48		$1,057.3152	$1,057.31	$1,057.35	$1,057.30