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	$32.54	10.256%	$35.8773	$35.88	$35.90	$35.90
Purchase #2	$93.60	10.643%	$103.5618	$103.56	$103.55	$103.60
Purchase #3	$128.51	10.412%	$141.8905	$141.89	$141.90	$141.90
Purchase #4	$40.51	10.317%	$44.6894	$44.69	$44.70	$44.70
Purchase #5	$62.37	7.316%	$66.933	$66.93	$66.95	$66.90
Purchase #6	$60.83	12.643%	$68.5207	$68.52	$68.50	$68.50
Purchase #7	$211.62	7.765%	$228.0523	$228.05	$228.05	$228.10
7 purchase totals =	$629.98		$689.5250	$689.52	$689.55	$689.60