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	$12.91	5.871%	$13.6679	$13.67	$13.65	$13.70
Purchase #2	$54.88	9.171%	$59.913	$59.91	$59.90	$59.90
Purchase #3	$138.26	3.148%	$142.6124	$142.61	$142.60	$142.60
Purchase #4	$172.56	12.866%	$194.7616	$194.76	$194.75	$194.80
Purchase #5	$113.45	8.829%	$123.4665	$123.47	$123.45	$123.50
Purchase #6	$250.99	6.704%	$267.8164	$267.82	$267.80	$267.80
Purchase #7	$250.25	8.516%	$271.5613	$271.56	$271.55	$271.60
7 purchase totals =	$993.30		$1,073.7991	$1,073.80	$1,073.70	$1,073.90