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	$71.25	13.577%	$80.9236	$80.92	$80.90	$80.90
Purchase #2	$66.59	12.208%	$74.7193	$74.72	$74.70	$74.70
Purchase #3	$35.74	13.379%	$40.5217	$40.52	$40.50	$40.50
Purchase #4	$29.82	10.577%	$32.9741	$32.97	$32.95	$33.00
Purchase #5	$168.82	11.359%	$187.9963	$188.00	$188.00	$188.00
Purchase #6	$61.75	9.194%	$67.4273	$67.43	$67.45	$67.40
Purchase #7	$141.29	9.708%	$155.0064	$155.01	$155.00	$155.00
7 purchase totals =	$575.26		$639.5687	$639.57	$639.50	$639.50