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	$47.76	9.709%	$52.397	$52.40	$52.40	$52.40
Purchase #2	$181.36	4.291%	$189.1422	$189.14	$189.15	$189.10
Purchase #3	$150.86	3.412%	$156.0073	$156.01	$156.00	$156.00
Purchase #4	$40.67	5.470%	$42.8946	$42.89	$42.90	$42.90
Purchase #5	$233.57	10.680%	$258.5153	$258.52	$258.50	$258.50
Purchase #6	$130.90	7.621%	$140.8759	$140.88	$140.90	$140.90
Purchase #7	$59.49	4.360%	$62.0838	$62.08	$62.10	$62.10
7 purchase totals =	$844.61		$901.9161	$901.92	$901.95	$901.90