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	$13.66	5.728%	$14.4424	$14.44	$14.45	$14.40
Purchase #2	$136.88	5.143%	$143.9197	$143.92	$143.90	$143.90
Purchase #3	$136.88	10.233%	$150.8869	$150.89	$150.90	$150.90
Purchase #4	$143.64	5.387%	$151.3779	$151.38	$151.40	$151.40
Purchase #5	$114.83	13.525%	$130.3608	$130.36	$130.35	$130.40
Purchase #6	$7.58	13.364%	$8.593	$8.59	$8.60	$8.60
Purchase #7	$79.38	5.342%	$83.6205	$83.62	$83.60	$83.60
7 purchase totals =	$632.85		$683.2012	$683.20	$683.20	$683.20