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	$23.98	12.295%	$26.9283	$26.93	$26.95	$26.90
Purchase #2	$47.74	9.817%	$52.4266	$52.43	$52.45	$52.40
Purchase #3	$78.90	12.142%	$88.48	$88.48	$88.50	$88.50
Purchase #4	$40.72	10.831%	$45.1304	$45.13	$45.15	$45.10
Purchase #5	$155.75	13.264%	$176.4087	$176.41	$176.40	$176.40
Purchase #6	$41.90	4.356%	$43.7252	$43.73	$43.75	$43.70
Purchase #7	$152.91	3.641%	$158.4775	$158.48	$158.50	$158.50
7 purchase totals =	$541.90		$591.5767	$591.59	$591.70	$591.50