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	$242.92	6.613%	$258.9843	$258.98	$259.00	$259.00
Purchase #2	$19.37	4.824%	$20.3044	$20.30	$20.30	$20.30
Purchase #3	$196.37	12.290%	$220.5039	$220.50	$220.50	$220.50
Purchase #4	$47.73	12.811%	$53.8447	$53.84	$53.85	$53.80
Purchase #5	$23.56	4.140%	$24.5354	$24.54	$24.55	$24.50
Purchase #6	$123.29	5.326%	$129.8564	$129.86	$129.85	$129.90
Purchase #7	$13.37	3.671%	$13.8608	$13.86	$13.85	$13.90
7 purchase totals =	$666.61		$721.8899	$721.88	$721.90	$721.90