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	$35.65	10.162%	$39.2728	$39.27	$39.25	$39.30
Purchase #2	$179.62	3.637%	$186.1528	$186.15	$186.15	$186.20
Purchase #3	$38.97	9.245%	$42.5728	$42.57	$42.55	$42.60
Purchase #4	$19.27	8.421%	$20.8927	$20.89	$20.90	$20.90
Purchase #5	$30.38	8.249%	$32.886	$32.89	$32.90	$32.90
Purchase #6	$24.58	5.279%	$25.8776	$25.88	$25.90	$25.90
Purchase #7	$48.49	11.257%	$53.9485	$53.95	$53.95	$53.90
7 purchase totals =	$376.96		$401.6032	$401.60	$401.60	$401.70