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	$227.93	12.254%	$255.8605	$255.86	$255.85	$255.90
Purchase #2	$198.88	12.291%	$223.3243	$223.32	$223.30	$223.30
Purchase #3	$183.86	13.193%	$208.1166	$208.12	$208.10	$208.10
Purchase #4	$100.88	11.868%	$112.8524	$112.85	$112.85	$112.90
Purchase #5	$11.80	10.199%	$13.0035	$13.00	$13.00	$13.00
Purchase #6	$185.49	6.173%	$196.9403	$196.94	$196.95	$196.90
Purchase #7	$115.91	8.514%	$125.7786	$125.78	$125.80	$125.80
7 purchase totals =	$1,024.75		$1,135.8762	$1,135.87	$1,135.85	$1,135.90