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	$75.40	4.229%	$78.5887	$78.59	$78.60	$78.60
Purchase #2	$18.52	12.822%	$20.8946	$20.89	$20.90	$20.90
Purchase #3	$142.46	9.298%	$155.7059	$155.71	$155.70	$155.70
Purchase #4	$95.82	4.462%	$100.0955	$100.10	$100.10	$100.10
Purchase #5	$210.98	6.373%	$224.4258	$224.43	$224.45	$224.40
Purchase #6	$140.88	11.219%	$156.6853	$156.69	$156.70	$156.70
Purchase #7	$9.59	11.392%	$10.6825	$10.68	$10.70	$10.70
7 purchase totals =	$693.65		$747.0783	$747.09	$747.15	$747.10