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	$23.95	5.518%	$25.2716	$25.27	$25.25	$25.30
Purchase #2	$221.39	7.811%	$238.6828	$238.68	$238.70	$238.70
Purchase #3	$249.32	10.802%	$276.2515	$276.25	$276.25	$276.30
Purchase #4	$247.67	12.789%	$279.3445	$279.34	$279.35	$279.30
Purchase #5	$112.32	9.615%	$123.1196	$123.12	$123.10	$123.10
Purchase #6	$215.38	7.177%	$230.8378	$230.84	$230.85	$230.80
Purchase #7	$114.83	10.376%	$126.7448	$126.74	$126.75	$126.70
7 purchase totals =	$1,184.86		$1,300.2526	$1,300.24	$1,300.25	$1,300.20