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	$112.71	6.388%	$119.9099	$119.91	$119.90	$119.90
Purchase #2	$244.98	8.159%	$264.9679	$264.97	$264.95	$265.00
Purchase #3	$144.61	4.697%	$151.4023	$151.40	$151.40	$151.40
Purchase #4	$30.33	3.612%	$31.4255	$31.43	$31.45	$31.40
Purchase #5	$99.92	3.615%	$103.5321	$103.53	$103.55	$103.50
Purchase #6	$155.93	10.213%	$171.8551	$171.86	$171.85	$171.90
Purchase #7	$58.33	7.798%	$62.8786	$62.88	$62.90	$62.90
7 purchase totals =	$846.81		$905.9714	$905.98	$906.00	$906.00