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	$199.49	6.615%	$212.6863	$212.69	$212.70	$212.70
Purchase #2	$174.45	9.323%	$190.714	$190.71	$190.70	$190.70
Purchase #3	$14.41	5.861%	$15.2546	$15.25	$15.25	$15.30
Purchase #4	$113.87	5.329%	$119.9381	$119.94	$119.95	$119.90
Purchase #5	$50.38	6.297%	$53.5524	$53.55	$53.55	$53.60
Purchase #6	$51.36	6.140%	$54.5135	$54.51	$54.50	$54.50
Purchase #7	$88.47	6.507%	$94.2267	$94.23	$94.25	$94.20
7 purchase totals =	$692.43		$740.8856	$740.88	$740.90	$740.90